The B grade pictured is a 1897-98 gun and so it has the older 3-piece lockplate design. There are photos of the shotgun on the Baker Collectors website that show the action from different angles.
The draw bolt was used on all guns in the Baker line regardless of whether it was the earlier lock design or the later 4 piece design. One exception is a later Paragon that came out in 1909... I've never seen any of the Model Nineteen Nine shotguns, but they reportedly did not have the draw bolt and instead used a second bolting feature running through the rib extension. I used to have a Folsom made Paragon and it did not have the draw bolt, but it incorporated a 2nd bolt that ran through the rib extension. That's the only Folsom Baker I have experience with.
I believe all of the Folsom guns had the 4 piece lock design. My Folsom Paragon had a slightly different shape to the lockplates, but still used the same mechanism.
The design change for the Model Nineteen Nine Paragon guns added a 2nd bolt that rotated vertically through the rib extension and was shaped to pull back and down on the extension. They eliminated the draw bolt because of this new way of securely closing the action. The cocking mechanism also changed to a roller cocking design I believe.
