As the improvements in design of the bolt plate (correct terminology here, please) were perfected, most guns sent back to Meriden for whatever reason were converted to the latest improvement in bolt plate technology as a matter of routine while they were in the factory (e.g., insert with planar shoulders, insert with sloped shoulders, etc.) without ever informing the customer who had returned the gun, and they were not charged for it. Let's just say it was Parker Bros. way of insuring forward thinking improvements in technology. Most people never detected the difference and to this day the different styles of bolt plate pinning, sloping, etc. are routinely seen on very early guns built after the non-insert era (e.g., static rear lugs which were simply machined at the correct angle for compensation for wear over time). Previous to the inserted (pinned) bolt plate, the only way to compensate for wear was to weld up the surface of the bolt sloped incline, then hand-file it to the correct tolerance. The bolt plate insert was indeed a milestone in prolonging the correct fit of the barrels to the standing breech, putting the gun (as our British friends say) "back on face."