As this is something of a hobby-horse for me, I've quoted below (with permission)a reply from Ron Gorow who has written a superb book on transcribing.
See www.rongorow.com for info
Start of quote:
"Like all notation, we're dealing with conventions, codes for the actual performance. Some of the swingin'est bands achieved it in spite of the notation (Basie, Woody, and an English band from the 1950s or 60s - Ted Heath. Ever hear them?
I've written charts in which there are both triplet figures and straight eighths. For instance, the first three beats of a bar are in triplet figures, then the 4th beat is two straight eighths, the last note an anticipation of a down beat. Again, subject to interpretation.
The transcriber's reasoning is anybody's guess. Keep in mind that music published before the 1980s (when the "rest of us" got laser printers) was carefully edited by traditional music editors who were very conscious of notational standards. A fake book, however, is probably created by some kid with minimal training or concern about notation. I created my own jazz fake book when about 20 but had the sense to not publish it. It was very valuable for my own training. In my book, I encourage you to transcribe and put together you own fake book, rather than buying someone else's interpretation. The experience of transcribing far outweighs the value of just owning a fake book.
Hope this clarifies.
Ron Gorow"
End of Quote.
The bit I think is important is paragraph 2 which at least explains how Ron sees the combinations being put to proper use. My best guess as to what the Fake Book transcribers are thinking of is the anticipation mentioned by Ron. On the other hand I might be being kind.