For my expanded monster list, I included all of the creatures with stats appearing in OD&D + Greyhawk, as well as most of the new monsters appearing in The Strategic Review (only leaving out the Denebian Slime Devil).
For aquatic monsters mentioned in OD&D vol. 3, I used stats from the Blackmoor supplement, and for monsters provided with only partial stats in Greyhawk, I consulted the AD&D 1e Monster Manual (the source of some creatures for the 2nd printing of Holmes).
A fighting man faces a group of monsters. Illustration by David C. Sutherland III, from the AD&D 1e Monster Manual (1977).