Someone asked me to fix this, and it is beyond my comfort zone. It looks like the same author, and should be combined; however, he has a different middle name/initial each time. It looks like there are issues with some of his other books, too.
I'll just post their PM to me:
This is the book on GRs (it is the same book, 2 different editions/formats, but shows up twice):
I'll just post their PM to me: