I own the 5E Monster Manual. I also have the Monster Manual I, code number 2009 from 1E.
I can see the difference between these two versions but I don't know what the other editions' Monster Manuals have to offer that's different.
As a DM or game designer, if I wanted to use the lore of monsters that existed in earlier versions of D&D (regardless of their stats since I can update those), is there any value in purchasing the Monster Manual for other editions?