In the example I showed yes, I made a different channel for the jam release (frozen version) and post-jam update (will be regularly updated - hopefully).
But I’m not creating a new channel for every version. For instance, when I release v0.6.0 it will override the v0.5.0, it’s really just for the jam release (or an important save-breaking change) that I do that.
Otherwise no, old versions are lost (https://itch.freezing.top/t/184990/can-i-download-older-versions-of-the-game, 7 years old but I don’t see a change in the interface so far), it could be a feature request though. For instance, add option to preserve previous version to butler, and show the list of preserved versions in itch client / game page “Show all versions” details?