the 1900 P Morgan double olive vam 16 is one of the top 50 vams. Well what about the 1900 O Siamese twin olive is that a vam also? Top 2 images the 1900 P bottom the 1900 O.
Second one is standard. It's an indicator of the c3 reverse design I believe. Here's a guide on how to identify 1900-1904 reverse types... http://www.vamworld.com/Reverses,+C4+and++C4C3+and+C3
Technically, all the C4/C3 reverses are Class III Doubled Die reverses (design hub doubled). The most dramatic for 1900 is the reverse of VAM 11 and 24, which is what those are in the Top 100. VAMs 16 and 18 were then chosen for the Hot 50, although neither is particularly rare. The C4/C3 reverses show up from 1900-1904. Other than the 1900 VAM 11/24 reverse, the strongest doubling is probably on the 1901 VAM 7 (1901 VAM 3 is a doubled C4 reverse). No matter how weak the doubling, you always see two distinct olives on the branch.