Mapbox Studio style rollback after a failed upgrade: what actually carries over to clients?

Mapbox Studio keeps a version history for each published style and offers a Revert/Restore option in the style editor. The scenario I am planning for is a style upgrade that introduces breaking changes to the style JSON, where rolling back to the previous published version is the recovery path.

The documentation and practical behavior leave a few points unclear for me. Reverting restores the prior style's source data, tileset references, and layout, but it appears not to affect map instances already loaded in client applications, and client SDKs seem to require a republish or forced style refresh to pick up the reverted version. I am also unsure how the version retention window (reportedly around 30 days) and the pre-2020 style migration requirement constrain whether a rollback is even possible when an upgrade fails weeks later.

My questions:

1. After a rollback in Studio, what is the reliable way to make already-running clients (Mapbox GL JS and mobile SDKs) load the reverted style rather than a cached copy?
2. Does restoring a previous version create a new version entry, and how can I confirm via the Styles API that the served style JSON matches the intended reverted version?
3. For styles last edited before the 2020 versioning overhaul, what migration steps are required before rollback becomes available?