Generally, when members dont opt in for the next season, they are removed from the Multisig when the new season of ACC is constituted. This was the process followed in S6 of ACC, which was the 2nd Season where the ACC was constituted following S5.
So in accordance, for S6 ACC the Multisig list was refreshed (old members removed, new added) and the changes are documented here.
In the Multisig, the transaction to update the signers was executed here.
However, in this case it seems that GFX Labs’ name was still appearing the “Form Responses” sheet i.e the list of members who had signed up for the S6 ACC by filling up the form for S6 ACC, collected by the Foundation. This form is then shared with the ACC Lead.
So one way to avoid this situation in the future is to maybe require Delegates who signup to the ACC to post publicly on an ACC Signup Thread a message like “I am a Top 100 Delegate and I am signing up for the ACC”. In this way, their response is documented and the ACC members can track the changes publicly.