I mean, if you’ve done something affecting upgrade paths - possible.
Also I broke a FreeBSD ufs partition once while upgrading OpenBSD. I thought I’m very smart having that added into disklabel, and it would successfully mount read-only. Well, there were some actions to upgrade OpenBSD’s own ufs partitions, so - I don’t really remember whether I could restore any data, TBF. I think I could still mount that read-only from OpenBSD, but not from FreeBSD.
I mean, if you’ve done something affecting upgrade paths - possible.
Also I broke a FreeBSD ufs partition once while upgrading OpenBSD. I thought I’m very smart having that added into disklabel, and it would successfully mount read-only. Well, there were some actions to upgrade OpenBSD’s own ufs partitions, so - I don’t really remember whether I could restore any data, TBF. I think I could still mount that read-only from OpenBSD, but not from FreeBSD.
But that’s about things being really broken.