Question relates to structure - the content below I don’t think provides spoilers as it is procedural and left intentionally vague.

After the intro mission there are story missions put in play based on narrative and one is selected.

once the first chosen mission is played - there is another mission added.

Do the original unselected missions remain in play alongside the new one or are they removed as they were in the Jabba campaign.

There seems to be an obvious omission. When a story mission result puts story missions in play, you should discard other remaining story missions first.

Correct me if I'm wrong, but nowhere it says to discard other story missions when a new comes into play. One friend of mine was saying that in JR's campaign, the book says to discard the others unused (I never played) while HotE was lacking this written on the book, so he had the same doubt.

Like I said, it seems an obvious omission in the mission results. (Although not that surprising, because there is very little space for mission rules left.)

You really should discard the previous ones. If the rebels choose "an old mission" you will get into a loop and run out of slots in the campaign log and the campaign will always end before the finale gets played. And then no-one wins the campaign.

https://www.boardgamegeek.com/thread/1881981/heart-empire-campaign-structure

They're discarded. If you're following the story what is basically happening is that if you pursue one mission then your next missions are the missions you didn't do but altered because the Empire has advanced their agenda in those directions.

It's a pretty neat way of doing things really, but I still wish it was a full length campaign.

yeah, for SANITY'S sake discard the unchosen story missions.

Thing is, story missions are largely balanced for a given threat level. You may or may not run into odd circumstances if you go back and play unchosen missions.

... besides, it adds the narrative flair and gravity to choices.

The next FAQ will have this rule of discarding the rest of the available story missions.