prosfilaes
Adventurer
Books that make revisions to the text rather than just correcting errors in spelling would have to have a completely new ISBN.
Who's going to make them? Seriously, you say "would have to", but Aerie back in the late 1980s-early 1990s, published a number of books under the ISBN 1559029838: Black Beauty, Three Musketeers, A Tale of Two Cities, Wuthering Heights, etc. This was exceptional; they were selling mixed boxes to Wal-Mart, so they didn't have to worry about individual ISBNs.
To take another, more minor example: all the errata at GURPS Basic Set: Characters, Second Printing Errata has been fixed in the most recent printing of GURPS Basic Set: Characters. But they're still using the ISBN, despite adding sentences and changing whole paragraphs. GURPS Cyberpunk is another examples; on top of the errata, the first printings came with the image all the way to the edge of the cover, and later printings switched to having a black border around the edge with GURPS and Steve Jackson Games outside the illustrated area.
The point remains: if a company wants to reuse an ISBN, the only issue is they won't be able to distinguish older and newer books under the same ISBN. If the only difference is a new cover and some errata, WotC may not care, Amazon won't, and the FLGS certainly won't.