I cannot find him mentioned in IMDB.

I skipped around some of the episodes too. Bingeing got a little boring on me.

It's probably S12 ep 21, the episode where Tramp disappeared, near the end of the series. He probably came back at the end of the episode. Charlie makes a doll for Dodie called Arfie, to take Tramp's place.

By the time season 12 comes around, it's obviously a different dog.