I hope that clarifies things somewhat.
Hi Chief (and all others who replied),
Thanks a lot: this indeed clarifies it. Now I understand the concept behind these "version numbers
". This completely satisfies my curiousity and was in fact the type of answer I was looking for. Does this for example mean that - when I download an new iso now -, it is called PCLinuxOS 2011-03 (or 04 for April). If yes I think I really understand the concept.
(I think that my download was more than a year ago - do not remember exactly - and since then I keep my system up to date.)
So thank you all for your answers and I'm happy now with Chief's explanation...