I believe that is the weight of the unstruck barrels.
Agreed. That is certainly the case with other makes, such as Fox. I am more familiar with the process used at Fox, than Parker, but would expect it to be similar. Oftentimes a set of Fox barrels will have very faint numbers. This is an indication that the tubes were struck off in varying degrees/amounts, sometimes in order to make the final weight of the gun equal to what was requested on the order card, or the range that a stock order gun was expected to fill. Sometimes the numbers are completely struck off and cannot be seen at all.
Rough tubes were evidently weighed, then marked in categories of weight. Ideally, when a barrel maker chose a set of tubes to build a gun to fill an order he would view the marks then choose the appropriate barrel that could be finished enough to yield a fine looking finish, with sufficient strength, but not have to spend days striking off excess steel to get to what he wanted.