MN list reconstruction relies on info not from the blockchain? Why? Doesn't that lead to a possible attacks?Not really, you need to reconstruct mn list which can't be done by using blockchain information atm.
Finalized budgets for past blocks don't matter, they are simply ignored.
How the past finalized budgets can be ignored if they are used to validate superblocks? I mean next situation:
There are 2 finalized budget F1 and F2. Amount of votes for F1 is bigger than for F2. So miner uses F1 to construct a superblock. But then someone issues additional votes for F2 (they can't be ignored). And any node will see that F2 has more votes than F1. And from this moment superblock for F1 becomes invalid (it uses incorrect finalized budget).