COMMERCIAL (BLUE BACK)
When NJ converted from the blue plates to the graphic plates in 1991/1992, there were some unused blue plate blanks left over.
Reflective sheeting was applied to the blue blanks, so we have some reflective plates with a blue painted back.
XY - XZ
XAJ2529 has an unpainted aluminum back.
The blue back commecrial plates appear to have started after the 7-digit series ended, so the first one was probably XY-10AA.
X10 - X99
The entire X10-A10 series was made on the blue plate blanks.
X-A - X-J
The X-1000A series retained the blue backs until at least the end of the J suffix.
X-1005M has an unpainted aluminum back.