Complex sentence: Because its distinct features are not apparent this variety sometimes turns up in every day collections, however this is unusual as the issues was printed in very limited quantities and consequently any surviving stamps of this variety are exceedingly rare and valuable today.
Split into simpler sentences: Because its distinct features are not readily apparent, this variety sometimes turns up in every day collections. This, however, is unusual, as the stamp was printed in very limited quantities and consequently any surviving examples of this variety are exceedingly rare and valuable today.