I'm not sure if this is the right term, but it seems like "interogative pronouns" like 何, 幾つ, 誰 and so forth typically have Atamadaka pitches officially in dictionaries.
Now consider the phrase
誰でしょう
According to the dictionary, this should be だれでしょう{HLLLLL}, and indeed here is an example of it I found in the wild: https://youtu.be/htycKsJg3KE?t=118 (1m58s).
Yet here are two examples of what sounds to me like だれでしょう{LHHLLL} (where 誰 suddenly becomes Heiban):
- https://youtu.be/OW_KFY4r_0M?t=162 (2m42s)
- https://youtu.be/pGt9IXTxiag?t=90 (1m30s)
As an another example, at 2m39s in https://youtu.be/HIqKOifGSAs?t=159, the speaker says
幾つありますか
with pitch いくつ{LHL}. But according to dictionaries it should be いくつ{HLL}.
Question: Am I hearing this pitch right? If so, is this part of a general pitch accent phenomenon? Does it have a name and a well understood pattern that can be referenced? To me it seems like Atamadaka "interrogative pronoun" words are becoming Heiban when emphasized in a certain way.