That line you see could be from where the collar is supposed to sit on the nib.
The hard rubber screw-in nib housing can be slightly shrunken heating it up with a hairdryer.
While the nib and feed collar is screw in, it is affixed in old pens with a sealant.
I think for most pens the 149 indicator on the nib is almost completely covered, but not on all my pens.
Thank you so much for your replies and recommendations! I have attached some more images below, my phone camera however is pretty horrible with focus.
The line looks to be where it once sat, however, you can only just see the 149 stamp under the collar lip. It is maybe half showing so impossible for my camera to take an image.
So to confirm, should I heat the nib/feed slightly and try to push in, or should I try and heat and screw it in? I tried both without heating and couldn't get it further in.