The Riverside varieties are quite old and were reproduced by grafting (that is, it is as if they were branches of the original tree). For example, limequat is from 1909, meaning any limequat tree would be that age. So a lemon from that time would not differ enough from a current lemon. Lastly, the seeds would not be viable, it is too old and citrus trees do not like the seeds to dehydrate.