Complex sentence: The Grove Library Collection of some 500 titles contains many of the incredible number of books Greve translated into German when he was Greve, & the FPG Translations Collection reflects an almost complete record of these titanic efforts.
Split into simpler sentences: The Grove Library Collection of some 500 titles contains many of the incredible number of books Greve translated into German when he was Greve. The FPG Translations Collection reflects a (nearly) complete record of these titanic efforts.