Complex sentence: These complicating factors demanded an unusual varieties of overprinted or surcharged stamps and over a long period of general usage these had made it very difficult to document early Chinese stamps comprehensively or by chronological order alone.
Split into simpler sentences: These complicating factors demanded an unusual varieties of overprinted or surcharged stamps. Over a long period of general usage these had made it very difficult to document early Chinese stamps comprehensively or by chronological order alone.