36' Navy with a plum extension

[RMF]

I came across a 36' dated S/42 with a very plum barrel extension. I have read that that later dated pistols (1939-1940) had this anomaly with the discolored extension but haven't seen anyone mention 36's as having it. This pistol looked perfect in all other ways (markings match, proofs were light but correct). An added benefit that this also was a N marked (rear grip) Navy and came with a Vogel Navy correct dated holster. Could the plum barrel extension on a 36' S/42 be correct? Thanks.