I relore things all the time, and for 5E I often use a lot of 2E lore for monsters over 5E lore as well.
For my homebrew
Ogres are the male offspring of hags
Goblins, Hobgoblins, Bugbears, Orcs & Trolls are from the dark dream area of the dream realm Aurora (there is no feywild)
Beholders were...