Complex sentence: Brendel recorded extensively for the Vox label--particularly his first set of the Beethoven sonatas--but secured a major recording contract only in the 1970s, nor did he play much outside Austria.
Split into simpler sentences: Brendel recorded extensively for the Vox label, and in particular recorded his first set of the Beethoven sonatas. He did not secure a major recording contract until the 1970s, nor did he play much outside Austria.