Its a real tag, the ZZ is done from behind, but it wasn't done on the same machine that did the rest of the trim tag data. The font is a little taller than the rest, and there was no provision in the tag machine to place characters in that location. The ZZ letters aren't as crisp as the rest of the tag info suggesting it was done either before or after the rest of the tag data was stamped on another fixture or by hand. Don't know what it means or when it was done.
In case you need a bigger image:
