The tang of the blade should not hit the 3rd pin post, if it does that normally means a problem with original scales...
Please do not take my word for this stuff I spout off, I learned it all by Looking at, and Measuring Vintage razors, so much so that I used scopes, and calipers to figure out WHY things were done certain ways...
Third pins add a different angle to the scales to accomodate tangs.. Sometimes I have thought it was for Etched and Decorated tangs other times perhaps an oversized or different taper to the tang... I have also thought at times they were simply decoration, it also adds strengh to the build,,, You want to really understand 3rd pins before they are added to builds because a missed sized one will do way more harm then good :(
But unless there was a problem with the scales (warped, damaged or bad pins) I never saw one used as a blade stop
edit: I just realized after writing this, inevitably someone will have a 3rd pin razor that rests on the 3rd pin post, please go look at a few more and see what you find :)