@lucy >you can't retroactively revoke a license like MIT.
MIT expat doesn't mention revocation, so there's a good chance it *can* be retroactively revoked.

The GPLv2 does not say it's irrevocable, but it does note termination conditions; "4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.", which implies that those who follow the license will not have the licenses terminated.

The GPLv3 is irrevocable; "2. Basic Permissions.
All rights granted under this License are granted for the term of copyright on
the Program, and are irrevocable provided the stated conditions are met. This
License explicitly affirms your unlimited permission to run the unmodified
Program."