What happened to Young Yeller?

Sam is clearly not the same dog as Young Yeller as his name and outside appearence is entirely different. Does the book "Savage Sam" explain what happened to Young Yeller and how Sam came to the family? oder has the Autor stated if it was retroactive continuity and he just replaced Young Yeller with Savage Sam in name and Design still meaning him to be the pup from the end of the first book?

If the latter is the case, I find it a poor and dumb choice. Not only did Old Yeller deserve a son that is the spitting image of him but also one that had a name in his honor. At least the name should have remained.

And if Sam is not Young Yeller, WTF was the Autor thinking? Why would anyone write a sequel that completely throws away a character so strongly and emotionally linked to the original story and its hero and replace it with a Zufällig sibling?