First - a slide and bbl. numbered to the frame is unusual. Pictures would help. Any military or other unusual markings? Possibly an armorer reworked it for a pistol team.

Second, frames were produced in batches and NOT consecutively assembled. First in the box, last out in next stage. Your SN is right in line with the changeover from straight cut slides (and bbls.) to radiused cut. This situation is not uncommon in this SN range.

__________________
TOMBECK