We've got the SL (Shure) versions - Countryman said there was no difference between the SL and L7 (Line 6) wiring, and certainly on their website the wiring diagram is identical.
Are you not thinking about the 4.7k resistor across pins 2 and 3?
We've had an issue with the B3 & B6 capsules (red and blue-band) distorting during loud musical theatre scenes, especially when they're positioned on the cheek (although we've experienced it in the hairline position too). It sounds more like digital clipping or limiting than microphone distortion. I've not quite been able to get to bottom of it yet - it seems intermittent. The Line 6 specs say to tie 3 and 4 for lavalier use and leave them open for instrument use, which isn't how most TA4 shure-wired mics seem to be from the factory.
I'd been through all of our B3 mics and soldered 3 and 4 together, and the next show I did was perfect. However we had the problem again with 2 out of the 14 systems we were using on a show last week. They started off fine, but after the first few scenes the distortion appeared. The same thing happened on the second rehearsal with different capsules, so we ended up having to patch in some analogue Sennheiser systems for those cast members instead.
I'm not sure what to try next. Judging by the TBP12 specs, it should be impossible to overload the inputs no matter how loud the cast sing! The receiver audio LEDs never get much further than 2 or bars, and I've never seen the red clip light on the beltpacks either. Puzzling!