TRAILER (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.
T-XA - T-ZZ
T651-WH has an unpainted aluminum back.
The blue back trailer started somewhere in the W-suffix series, between WH and WZ.
T1A - T9Z
The entire series from T1A-100 series to T9Z-999 probably has blue backs.
Verified up to T9X-990.
T18-A9N has an unpainted aluminum back.