Vented rib not mentioned in serialization book…

[MrBojangles]

I think it appears like the one that has the added rib. I recall the fluting on the side and the divot in the rib extension, as well as not recalling the lack of concavity in the frame, but I could be wrong with regards to that as this one is more subtle.

I assume the work would have been done by Parker, as the appropriate barrel markings are present. And how would that affect value?

[Bill Murphy]

A Parker with a factory installed vent rib after the time of manufacture has almost as much collector value as one with a vent rib from the time of manufacture. My opinion only.