Complex sentence: For nearly fifty nears after his death, his heirs did not circulate his work at all, and it was not until the mid- 1960's that many of them became available for sale for the first time after the last of his direct descendants died.
Split into simpler sentences: For nearly fifty nears after his death, his heirs did not circulate his work at all. It was not until the mid- 1960's that many of them became available for sale for the first time after the last of his direct descendants died.