As you say, for that to have any value, Pprune would need to put in place a checking system on what people declare. I doubt that the CAA/FAA would be interested in supporting that in the way you hint and who will pay for that, then?
And why stop at pilot qualifications? I'd like to know people's age as well. And their ethnicity and country of birth so I can give those who do not have English as a first language the benefit of the doubt and add a degree of interpreting w.r.t. cultural background.
And gender, of course, not to mention sexual leaning.
All of which Pprune would need to check?
I know, reductio ad absurdum, but why should Pprune offer any more guarantees regarding qualification than you would get in real life if you hear people talk together in the pub?
Oh, and quite a few CPL/ME/IR/ATPL talk as much carp as some of the students. Argument by authority is rife here (and elsewhere, for that matter)
You get to know posters. Sometimes you get it wrong. Just like real life - where there are no certainties either...
B.