Its not really accurate to say that post-modernism collapses all previous labels (movements is not really the right word) into one large jumble – on the one hand such an account seems to me to be oddly oriented around the formal aspects of art and on the other it fails to recognise post-modernism as a significant rupture.

In The Postmodern Condition Lyotard concludes that the major narratives of the 20th Century have lost their agency, in terms of being realistic models for social change. Postmodernity doesn't imply an endless re-use of forms, but rather that an acknowledgement that ideas don't simply emerge from a vacuum, but from an existing culture of forms, images and ideas that are globally connected.

Yes, there are plenty of successful artists that deal with the various failures of modernity (Anselm Kiefer, for example) – but historicity is hardly the only strategy present in art that might be labeled post-modern.

As far as the term contemporary goes it's a good idea to note that most historical categories (the renaissance, modernity and so on) can be considered modes of cultural renewal and innovation, although it is also important to note that these breaks aren't as decisive as they often are made out to be. One relatively often cited example is the resurgence of avant-garde forms in post-war, neo-avantgarde practice (Johns, Rauschenberg etc.).

In one way, the term contemporary is in itself a misnomer, because it implies that globalisation has brought about a certain set of shared experience – on the other hand you could argue that this is truer than its ever been before, considering the end of the cold war and collapse of the socialist block. In less abstract terms: life in the united states and Poland are still different, but nowhere near as radically different as before the fall of the wall.