> "Must have had been" is simply wrong; in your examples, it should always be "must have been".
As a matter of prescription, maybe, but as a matter of description? I think it's interesting. It is meaningful and it's something that English speakers produce. Here are other examples in the wild:
"To complete the request, the owner of the permit must have had been present at the time the citation was written, present a valid permit to the Tax Collector in person, have a copy of their citation, and pay a $7.50 processing fee to the Tax Collector if approved."
"Lankeshwar must have had been easy to defeat compared to new-age Ravanas."
It can even have a distinct meaning (rather than just being a variation), which is how I would interpret it. Which I think is cool.
It's perfectly fine to say "don't use this construction if you want to be taken seriously by so-and-so", but if its usage happens to be dialectal, for example, I don't think you can say those speakers are using their dialect of English incorrectly.
As a matter of prescription, maybe, but as a matter of description? I think it's interesting. It is meaningful and it's something that English speakers produce. Here are other examples in the wild:
"To complete the request, the owner of the permit must have had been present at the time the citation was written, present a valid permit to the Tax Collector in person, have a copy of their citation, and pay a $7.50 processing fee to the Tax Collector if approved."
"Lankeshwar must have had been easy to defeat compared to new-age Ravanas."
It can even have a distinct meaning (rather than just being a variation), which is how I would interpret it. Which I think is cool.
It's perfectly fine to say "don't use this construction if you want to be taken seriously by so-and-so", but if its usage happens to be dialectal, for example, I don't think you can say those speakers are using their dialect of English incorrectly.