Most probably the filesystem is updated (silently), like it happened historically.
In the good ol' times there were free demo CD's of Windows 2000 (90 or 120 days trial), everyone (that was running NT 4.0) tried them.
Those with NT 4.0 already up to SP 4 had no issues (but chkdsk stopped working) all the ones with earlier service packs had unbootable machine (if the NT 4.00 was on NTFS).
At the time there were a couple "workarounds" for the CHKDSK issue, one by Sysinternals/Mark Russinovich NTFSCHK and one, Mark4NTFS by M. Tartsch.
In the good ol' times there were free demo CD's of Windows 2000 (90 or 120 days trial), everyone (that was running NT 4.0) tried them.
Those with NT 4.0 already up to SP 4 had no issues (but chkdsk stopped working) all the ones with earlier service packs had unbootable machine (if the NT 4.00 was on NTFS).
At the time there were a couple "workarounds" for the CHKDSK issue, one by Sysinternals/Mark Russinovich NTFSCHK and one, Mark4NTFS by M. Tartsch.
Just in case:
https://msfn.org/board/topic/169500-chkdsk-refuses-to-check-...
But no idea if the mark4NTFS can help for NT 3.x.