Wraithbone Singers says:

" When you purchase a structure while resolving this order, you may place that structure on a friendly world that already contains exactly 1 different structure."

Does this allow a player to build a second factory on a world? In other words, does "different structure" mean "different type of structure" or "other structure" in this case?

And if you can't make two factories, what is this all about under factories in the rules reference, p 7:

"Some cards allow a player to have two factories on the same world. That world’s unit capacity is doubled when determining that player’s deploy limit."

Different structure means no duplicating what's already there, so no second factory for example.

The RRG quote mentioned could come into effect from other cards,like the space marine "Direct the Faithful" that allows you to change a structure type if they already used "The Emperor Protects" and had two structures on a planet. So it is possible with some cards to do it, just not from Wraithbone Singers.

Hope that helps!

This gets asked a lot... but how can this be confusing?

"red is a different colour to blue"

"A bastion is a different structure to a city"

The card is saying you can use this card to target any planet that has already got ONLY 1 structure, and build on it any structure that is already not on that planet.

The confusion I think comes from the two factory thing... but this is not really confusing. The "golden rule" applies. It doesn't matter what the manual says, the card over rides it and the card is extremely clear here.