Ringo-
So based on the figures you came up with, you are saying to use the low limit of the thinner piece and the high limit of the thicker piece, which essentially gives you the widest range of thickness qualification. I think where the confusion is, there are two pieces of different thickness, and 17.1 doesn't clarify whether to use the thick, or thin piece to qualify range, and it doesn't say to use a combination of the two, but then again, it doesn't say you can't do that either. Depending on the interpretation, which could potentially get someone in trouble, it could mean many things. It is bit confusing.
EDIT:
Here is a hypethetical question.
The two pieces of material we have been discussing are relatively similar in thickness, and their range of qualification overlap eachother drastically. If you had for example, a piece of 1/16 wall tubing welded to a piece of 1/2" plate, now you have a situation where the range of qualification wouldn't overlap. So my question is, would the thickness range of qualification be divided to two ranges, (.042"-.250" and .355"-2"), or does one thickness take precedence over the other?
Jason