This is not correct. = means spare, but this is a port adapter and they'd all be spares unless you bought a BUN, right?
In this case the + means it's the enhanced version. The PA-T3+ and PA-2T3+ will support Kentrox signaling "dsu mode 1" with subrate timing for fractional T3 service. This is NOT supported on non+ As far as I know that's the only difference; however, the non + unit is EOL.