Defender reciever and slide tags

[HaulRoad]

Does anyone know the purpose or meaning of the various numbers stamped on a Defender?

I see a:
0 on the left side of the trigger guard
1 above the firing pin on the slide
2 on the front right side of the trigger guard
and some other kind of proofing or stamp on the left upper front of the trigger guard.

any takers?

[X-Mark]

The #1, on the firing pin stop, is put on ser. 80 stops...