Multiple versions of old prerelease cards

There are two instances of some of the first prerelease cards printed of which there are two different versions, but until now I have not been able find the reason/story of why a second version was printed for those! Maybe different regions? different events?
Is there any MTG archivist that can share this piece of game history?

Dirtcowl Wurm (Tempest):
- V1, stamped in the middle part of the frame
- V2, stamped in the lower part of the frame

Lu Bu, Master-at-Arms (Portal Three Kingdoms):
- V1, stamped April 29, 1999
- V2, stamped July 4, 1999