Jim,
The Parker btfe that you pictured as an example is one of the other styles that Parker made. The one on the gun in question is another style. In fact, there are parker catalogs that picture the exact style of forend that is on the gun you were looking at.
You will also find, if you look at enough live bird guns, that the filled safety slot is very common on guns ordered without safeties. Not many built without safeties actually started life as not having the slot cut in them.
And, the extreme rarity of it having a vent rib alone makes it worth the price of admission.
Take some time and study up on Parkers if you are looking to learn on them and buy one. A copy of The Parker Story would be a great start, or even one of the earlier books written on Parkers.
