But why is an explanation even necessary or required or desirable? Trek should be about new ideas. New life, new civilizations and all that. Devoting a large chunk of a season to naval gazing over a simple change of make-up is missing the point of Star Trek. As Gene Roddenberry said, a policeman in a cop drama doesn't stop to explain how his service revolver works.
Kor Was a Klingon, Worf was a Klingon. No more explanation is needed.
The novels are free of the budgetary limitations of a TV series and yet people still want to go back to the same old trough for another drink. If you're going to beting back an old element, tell us something new, don't just try to explain away a costuming change.
The Final Reflection dealt with this issue by showing us HOW the differences affected the Klingons, not just trying to tie it all up on one big, small universe bow. It didn't go into excruciating detail trying to get it all to fit with other parts of canon. That brings us to the pint where pretty much every big event we've heard of involves a ship Named Enterprise or a crew that had their own TV show. That was the one failing of Vanguard. It reduced a fascinating new crew to background players in their own series by making the events of TOS the big story. Almost everything the ended up doing was putting pieces in place for JTK and his crew to play with sometime down the line.