SA 1911-A1 Serial Number Question

Saw an older SA 1911-A1 with (on the original box and on the frame) a serial number NM150???X ('95ish mfgr. date). I thought this was unusual as I never heard of an "X suffix" on a SA 1911-A1. Was this a custom shop addition, or something like that? The X added was definitely post-parkerizing...you can see a plain shadow of bare metal around the "X".

An X sometimes represents a duplicate serial number....yes it does happen.  Calling Springfield and asking is probably the better way to "know for sure".  bob

I called them...they did not have an answer. I'll try again.