Some things that I noticed...
First off - Tom Seaver was a Yankee broadcaster during 1990, so I'm not sure he would be at Mets camp early in the year. Second of all, the Mets did not wear game jerseys in Spring Training (at least not until this year).
Third, every legit game used jersey that I've seen from the 1990 season has the strip tagging underneath the Rawlings tag (I have some pictures of examples that I can post when I get home). These appear on common players (like Darren Reed, Phil Lombardi, Chuck Hiller), which further reinforces this point. Fourth, the name looks a little spaced out and "flat" to me. It doesn't look right for some reason when compared with other jerseys from that year. However, the embroidery and tag style does look correct. Strange. Just my 2 cents!
Chris