Adam France said:
That simply doesn't work imo. It seems to me like a clever idea that hasn't been properly thought through.
The constellations being different doesn't really matter in itself, because soldiers wouldn't know the different between constellations in the Eastern Rim and constellations in the Margin.
There are however at least three much more obvious reasons why that secret wouldn't work and couldn't be kept.
1) One of the three salients is being fought against the Tau. That's the Tau specifically limited galactically to the Eastern Fringe. All the Crusade Army would have to know the Tau are one of the three enemy forces - now they could assume 'heck the Tau somehow are able to get from the Eastern Fringe to the Calixian Halo Stars! Whoa! That's amazing.' However added to the 2nd and 3rd reasons (and the few knowledgeable people who can stargaze) it doesn't really make sense they wouldn't also wonder, or actually realise, that they themselves are in fact on the Eastern Fringe.
2) There's a stonking great, named, Chaos Storm-thing, at the centre of the Crusade region and on the map - that's the regional map which only shows the really well known planets and stuff of the area. That particular Chaos storm is as we know on other galactic maps ... located in the Eastern Fringe of the galaxy near Tau space. Hmmm.
3) The Margin Crusade is previously stated to be being fought beyond Kalf, beyond the margin of the Imperium (which Calixis is right on the outer edge of), and beyond even the light of the Emperor (that's stated in IH). So soldiers sent to the Margin Crusade rightly would expect to be fighting on worlds that have never known any significant Imperial presence and which certainly have never been a major part of the Imperium, or a wealthy Imperial Sector ... like say the worlds of the ... Jericho Sector. The Jericho Reach worlds must be covered in Imperial ruins ... all of them. Now even if there are only ruins left, and not stores of data-arks, cogitators, statues, books, records, etc etc (which isn't imo credible), it would not take anyone with half a brain long to start seeing references to world names, that can be looked up at the first opportunity.
ALL armies thrive on gossip and rumour. This secret would not hold. Imagine Gaunt's Ghosts going into this one, Gaunt would have it solved inside one book. Heck it wouldn't take a genius.
Also it wouldn't take the enemy forces many prisoners to twig they all seem to be from Calixis, Ixaniad, and Scarus, on the other side of the Galaxy and all believe they are fighting in the Margin, not the Eastern Fringe. Also I'm not really convinced Lord Sector Hax (or the Scarus and Ixaniad) leaders really get much of a say where their soldiers serve in the Galaxy anyway.
It simply does not work.
I sure hope as well this doesn't mean we won't ever learn who the Margin Crusade was actually being fought against. Or at least if that is going to be the case, that we can be told we won't ever be told, so I can make it up myself without fear of official contradiction.
As a personal taste issue, I also don't like this idea because it means the Margin Crusade is also being fought against Tyranids in 815 (assuming that is the case?), and I firmly believe and prefer the much more internally sensible and consistent canon that states the Tyranids were believed extinct after Macragge and before the arrival of Kraken in 992.
I personally think that this could actually work quite well. I understand your reservations, but I think that logically there are just as many reasons why it could work very nicely.
The constellations issue doesn't worry me in the slightest. Even moving from one world to another in the same subsector would totally change the layout of the night sky, and perhaps only a Navigator or lifelong astronomer would be able to identify galactic location from the stars on a random world's night sky.
The Tau point is IS harder to reconcile. However, I think you're making a number of arguably erroneous assumptions about the way news about a crusade filters back to the Imperium, and the level of galactic knowledge held by most of its inhabitants. To successfully identify a Tau AS a Tau, and from there to identify which part of the galaxy it lives in would be beyond the abilities of all but those who have the Forbidden Lore (Xenos) skill. Remember, this information is called "forbidden" for a reason. The Imperium actively discourages the study of this field, except among its elite operatives. So 99% of those involved with the crusade wouldn't really have any experience of or knowledge of the Tau, and you can imagine the 1% would treat it as Top Secret. Also bear in mind that there are so many local xenos races which resemble the Tau. Unless you were very knowledable, you wouldn't be able to spot the difference between say, and Enoulian (Calixis-locale Xenos race) and a Tau (Eastern fringe Xeno race).
And as for the rumour and gossip thing among crusade forces, yes, I accept that this would be rife. But how does news actually pass among regiments scattered across dozens of light years? The only way of even passing data at this level would be by using Astropaths, and their information would be tightly controlled by High Command and the Inquisition.
I accept that maintaining this facade would be harder among the Imperial Fleet. Officers there would likely have a better idea of the enemy they are facing based upon records of alien ships. But it's quite possible that only the top 20-30 officers in each ship (plus astropaths and navigators) would have this information, and they'd be under no obligation to pass it on to Imperial Guard officers. Plus they've likely been ordered not to.
As for the chaos storm thing, bear in mind that as readers of 40k material, we know far more than the inhabitants. Your critique of this point is that crusaders should easily draw a connection between a warp anomaly in their area of activities and a warp anomaly on maps of the galaxy. When would the average 40k inhabitant have access to maps as detailed as the ones we (as 40k consumers) have? And it would also seem that warp anomalies are relatively common: Rifts of Hecaton, the Cauldron, the Maw....All of these features appear in the Koronus Expanse alone, and I can think of two others (Eye of Terror, Maelstrom) just off the top of my head. All warp anomalies are weird, but knowledge of which one is which would imply possession of a combination of the Forbidden Lore (Warp) and Astrography skills. Most people in 40k wouldn't have that sort of information.
As for the Margin Crusade/Imperial Ruins issue, I concede you have a point here. But if you're an Imperial Guard Colonel and you find yourself fighting through the ruins of an Imperial Cathedral, what do you do with this information? Maybe you pass it up the chain of command with a query as to the history of the world you're fighting on...you'd probably get a strongly worded missive back telling you to roll your neck back and concentrate on following orders and not to speculate about anything above your pay grade. And who would you voice your suspicions to? Perhaps other officers... Maybe even some of your trusted troops. But what would you do with this information really? Raise a formal complaint with your Commissar about being lied to by High Command? Er...not if you've got any sense. So what do you do? You curse about the quality of the Intel you're receiving and carry on fighting... Like soldiers have always done.
Although there may be sporadic questioning of the "Official line" about fighting in the Margin Crusade, I think that the Big Lie would actually hold up pretty well.
The Tyranids thing IS a point, though. Perhaps (and here I engage in speculation to support a setting which Adam sounds like he already has reservations about) the classified nature of whatever the Crusade is ACTUALLY about means that the Crusade High Command doesn't want the wider Imperium knowing about what's going on in the Jericho Reach? I know Adam'll hate that explanation, but it's just a thought...
EDIT: Plus, as an obvious 40kRPG crossover point, it means that all 3 games can be run in the same setting. A character could start in the Calixis Sector, move to the Koronus Expanse and end up in the Jericho Reach. Plenty of crossover opportunities without stretching things too much. Though I know not everyone will agree with me on that.
Well, if that doesn't beat all...