Jay,
I got the book, too and have read it, in part wondering about their take on OCC as well.
While not definitive, a listing in 1924 but not subsequently may support the notion that LM did OCC. Granted, this is all speculation, but I say that because:
Its possible that Stiles thought he had a contract at deadline for submitting his list.
He may have actually had a contract, but missed a construction site visit due to distance or schedule. OCC may have decided a closer gca would service them better and selected LM.
Or, maybe Stiles even did some design work but couldn't handle construction well ( a la Ross after WWI) and farmed the work to LM. Even more likely, who ever got the construction contract ( American Park Builders (or others) might have brought LM in to finish because of a past relationship. Maybe Stiles did just the routing.
Yes its speculation, but those things still happen. With some confusion over 80 years, it makes sense to me that something unusual happened to create it.
The on site evidence that its Stiles, BTW, is that the remaining original greens as of a few years ago didn't look completely like LM greens, although a few did. I am not an expert on Stiles, and am going from memory, but more looked like the photos in the book than the most dramatic LM greens, and the site would have afforded LM the chance to do more boxcar greens, etc. that they were famous for.