Alright, I want to make sure I've got this right. Even with FAQ 2010 things are confusing.
So spores (in addition to their turret role) are supposed to work like shields. So the bit about them regenerating at the start of the turn isn't accurate, the regenerate when the ship moves off of any blast markers/gas clouds/etc.
So if a squadron of six escorts goes all ahead full through a typicall battleship the first four would leave blast markers, knocking down its shields, and the next two would score automatic hits. Eldar, necrons, or enemy kracken would just take automatic hits and make their saves for all six, but would NOT have blast markers put down.
In either case, if the tyranid escorts move beyond the enemy ship then they would no longer be touching blast markers and thus their spore cloud is once again at full strenght right? So in principle if they then go over a cruiser behind the battleship they'd put another world of hurt down, and if they still had movement, would once again be at full strength once they got clear and be ready to gun down some torps they run into on a 4+ and be ready to get shot on the opponents turn.
Also it just happens once per contact. For exampe a hypothetical squad of six tyranid cruisers would do the exact same things as the escorts as far as spores go.