[TPIN] Bach question

[David Johnson]

I have an question for the Bach experts.

I am trying out a Bach Strad sn 4xx,xxx. The second valve casing is
clearly stamped with an "L" indicating a large .462 bore. The bell is a
37, however, which is an unusual combination, right? I also have 2 other
Strads, a regular 37 lightweight and a Vindabona, and the tuning slides
from the large bore horn are virtually interchangeable with the two ML
bore horns. I don't have any accurate measuring device, but the inner
diameters of the slide tubing seem to measure the same (as measured on the
shank of a trombone mouthpiece). So what's up with that? Is it mismarked?
Is this another testament to Bach's quality control? BTW, the horn does
play very well. I was just looking to try a large bore horn, having played
medium bore horns for years (Connstellation, Martin Committee and Yamaha
Bobby Shew). Am I missing something here?
TIA.