>>281562659
I think they'll be mostly chosen from already released episodes(up to vol 22), since mllsd's adaption has the purpose of being the easy and quick to make stopgap.
Considering act 1 has episodes from vol 1~6, I think later acts will have more recent episodes(in fact mary and ogin are confirmed, meaning das finale episodes will be made as well). Act 2 could cover episodes from vol 6~11, act 3 could cover vol 12~17, and the final act might focus on the newer episodes.
Although the episodes published after the announcement are unlikely to be included, they may still have a thin chance to be included since the mangaka also worked with the anime staffs. Who knows if the mangaka made some episodes in advance for the anime and released them later.