Do a Google search for "remington shotgun proof marks". The images there explain all of the possible Remington proof marks, which include the ones on your photos. They are not double struck, it depends at which stage the barrel was made which sometimes makes the mark to be raised.

 

Proof marks should be slightly raised. If not it means work was done to the barrel after it was proofed. Could be as benign as a reblue.

The left side markings left to right, the inspectors stamp, 'R' - made in the month of November, 'Y' (?)made in the year 1974, '5' Assembly #

The right side markings 'REP' - is the Remington Proof mark, the others indicate magnaflux and test.

Remington barrel markings while accurate for the barrel do not mean the barrel is the original to the shotgun.

If the barrel was ever repaired by Remington there would be additional markings on the left side.

This is the link to Remington barrel markings.

https://www.remingtonsociety.org/manufacture-dates/