I have never seen this in fact, in spite of have examined literally dozens of Model A's at gun shows. I've seen have the lower lip milled off the face of the bolt. The sights on the model B are different from those on the Model A. 1. Elevation and windage are adjusted on the front sight, and requires a SMG sight-adjustment tool. The sights on the Model B are adjustable without a special tool.
Elevation is adjusted on the front sight and windage is adjusted on the rear sight.
And of course the blocking bar in the the receiver and in the trigger group are the same on both models. And FYI, the pin that holds the trigger group to the receiver is a larger diameter on the Semi than on the SMG, so the various SMG trigger groups for sale in the Shotgun News will not fit the semi gun without modification. Hope this helps. Posted by Wm. IMI semi UZI's, and yes they all had closed bolts.