Re 8dn, I think Srinivasaraghava misses Rishekesh’s point. For the clue to be correct as it stands, it is not necessary that all guides be Sherpas but it is necessary that all Sherpas be guides. (Whereas in fact some Sherpas are people who do not work as guides while still others are British Leyland vans!) A question mark might have been used to indicate that the answer is more general than the definition would otherwise imply. Thus if the answer to a clue is Toyota, “car” is an adequate definition, but if the answer is “car” the definition needs to be something like “Toyota maybe?”

As you say, 13ac cannot be found in any of the usual references but it is in Brewer’s Dictionary of Phrase and Fable.

I assumed 21dn was a reference to the character in one of the 007 films as I cannot find it defined as manservant in any of the three Cs.