In a recent gap fill exam in my university, students were asked to choose the correct form of the verb "suffer" to complete a sentence essentially the same as the following. (Neither the previous nor next had any time expressions or clauses.)
Dr. Jones says that more and more people ___________ from sleep deprivation.
The most obvious answer is "are suffering", which is unquestionably correct. This was in the original answer key.
We queried whether or not "have been suffering" and "suffer" might also be correct.
"suffer" was accepted, but "have been suffering" was rejected.
My argument for allowing present perfect continuous was that although the sentence contains no time expression "more and more" implies a recent change/development. However, I've been unable to find similar examples. Any example I've found where "more and more" is used with PPC had a time expression such as "these days" etc.