[Legogris]

They would still have to go back to past contributors prior to introducing CLA.

Source: My PR was merged in 2021, the changes are still part of Synapse, and I never signed any CLA. I don't think they'd be able to get enough sign-offs from historical contributors to pull off any actual shenanigans with the Synapse license.

[Arkanosis]

I understand that pre-fork code is under the ASL, not the AGPL, so anybody can use it within derivative works under any license — no CLA needed.