JKJBlue,
Sorry for the delay. Your stamp is very interesting and I wanted to ruminate and research more. The first stamp.
1. This is typically a very difficult stamps to distinguish apart. #1 and #15A (and #15Ac) are sort of coin tosses, and a classic puzzle for Newfies.
2. The easiest way is if you have comparisons to authenticated examples, and I have done this with mine--years ago at a dealer with Cherrystone. Because then you can see and touch real examples. I'd recommend considering this at a stamp show or a dealer--it can be fun to share and informative
3. That aside, in my opinion, the paper differences are the key, as color's can fade. #1 is thick paper and white. It is thick so that if you hold one corner with the tong, and gently flick the other corner with you index finger, you will feel it move differently. sort of like a postcard--so they paper moves stiffly. the #15A and #15Ac is dull yellow white paper and with the same technique above, it sort of flutters like a feather--or the NSSC describes it as "snapping".
4. Turning next to color. A good color chart can be a great way and in combination with paper pretty solid. but these stamps are 150 years old and colors change, eh? The #1 is listed in Unitrade as "Brown Violet" but the NSSC uses "Brownish Claret" instead. Go figure. The #15A is "Violet Brown in both". The real curveball is the 15Ac which is "Chocolate Brown". To me, the #1 and 15Ac look more alike with more red/violet than brown.
5. Mesh. For me this is hard and less reliable. My understanding is that #1 has crosswire mesh and the others just mesh.
6. Date. Clearly having a cover with it would be definitive way to ID them, because the #1 was in 1857 and the 15A/15Ac were in 1861. Best not to throw away covers, IMHO
7. Watermark. Not my standby nor expertise, but the 1 does not have one. The 15A/15Ac have a two line "Stacey Wise 1856" but not on ever stamp (which is why I don't use it).
All that, my opinion is that your 1st stamp is 15A. I LOVE the cancel; sort of uncommon I think
Your second stamps is either 15Ac or #1 (depending on the paper). If it was me, i'd lean towards it being #1. I do have a caveat. At my first impression, I felt that your second stamp presented falsely. It just felt too colorful. Too nice for the age. Looking at the back, it is so white and while there is a thin and some colorization, I just wondered. Where is the cancel? Also, look at the margins on the front, they feel so precise when compared to the first stamp, which had irregular straight edges. As I looked at it more, my feelings subsided and I think it probably is genuine, so not worth having any alarm; still I figured you'd want my feelings to take with a grain of salt.
Here are images of my three stamps (#1 on top row; #15A and 15Ac on second row)
