You can see some watch with a chapter ring completely cut for date window, thus looking like a “C”. Is it a franken with non date polerouter? or is it still legit ones?

 

I think the early Polerouter Date models had rings that had complete cut-outs for the date window (your second image above).

I think later Polerouter Date models had rings with partial cut-outs (your first image above).

Polerouters (no date models) should not have any cut-out.

Apologies if I've misunderstood your question.

 

The 204503 and 204504 (besides the (-2BD) had a non-joined marker ring, like in your second photo.
This is because they used a 215-1 movement, where the date ring was further out from the centre of the movement.

When UG changed to the new 215-2, the date ring moved inwards a few mm, and the marker rings could be joined at the edge (like in your first photo). This type of marker ring continued through into the 218-2 and 69/1-69 powered movements.

 

This information is such a WOW to me. Thanks for the lesson. So, is it reasonable to presume dial part of 215 and 215-1 is not interchangeable with later movement?

 

A lot of parts are interchangeable between the 215, 215-1, and 215-2 (they are all 215-based after all).
The main differences are in the addition of the date mechanism addition, which was not there for the 215, and different between the 215-1 and 215-2.

If you look on Page 2 of the Technical manual, you can see the main differences between the movements are shown (and Page 3 shows the parts difference between 215/218 and 215-2/218-2).
https://universalgenevepolerouter.com/vintage-technical-manual/caliber-215-x-218-x-138-x/