neither the exact angle of the dove tails , nor the amount of taper of the lid and ways in the stock, are all that important. the dovetails only serve to hold the lid on the stock when in place and the taper just makes the lid separate from the stock easier with less rearward movement. just a decent amount of angle that won't be forced out of the ways when in place and enough taper to make the lid sit in place as you put it on the stock is all that is necessary. it is much more important that you get the angles of the dove tails the same or very close between the lid and the stock. the closer the angle match, the more securely the lid will stay on the stock without trying to slip by the ways. the deeper the engagement of the lid and ways in the stock and the amount of taper in the design, controls how far you have to back the lid up to have it detach. one other thing to consider is that you make the lid out of fully cured wood, so that, later down the road, there is no chance of shrinkage allowing the dovetails to slide by each other when the lid is all the way on.
I would assume that various schools had a "typical" angle and taper that they preferred as a standard, but it's importance to the gun is minor, in my opinion, because this detail, being done completely by hand, was most likely done by eye and slightly different on every build.
