MAZ-2321 strike designation

Hey guys, recently I acquired this 2 centimes piece which I understand to be an essai. The confusing thing is that those graded by NGC(such as mine) are designated using MS, as opposed to those at PCGS with SP.
I was wondering what the difference was? Also, if anyone has some background information on this particular type of coin I would love to hear about it as I don't think it has been listed by Krauze yet...
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There is probably no difference. PCGS routinely give the SP designation to patterns, essais, and medals. NGC does not, but will use MS or PF depending on the situation.
I don’t know anything about the issue, but if you’re going to collect these, I highly suggest you get the Jean Mazard reference. It’s technically obsolete, replaced by Gadoury, but it’s really a great book (or should I say, pair of books). A bit expensive since it’s a bit scarce.