Mexican notes attribution assistance

[Techwriter]

"Found" a couple Mexican banknotes; my records show zero, not where I got them or what I paid or the Pick number. Well, in my Krause SCWPM hunting I've narrowed it down but am uncertain as to which variety for each.

Your assistance is greatly appreciated. Here's what I have determined:

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== S551, however, Series S not noted in SCWPM

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== this is an S631 not sure of variety

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[JLarronde]

On the S551, can the back seal be a little bit green-ish? it is maybe a S551i?

 

On the S631 I don't know about any variety difference. Did you see any with one?