My customer is currently using the TI part TLK6201EARGTT and TLK6201EARGTR and ramping up to do a last time buy on these parts and noticed something per the spec sheet: 
The “TR” part is listed as MSL 2 and the “TT” is listed as MSL 1. Why is there a difference in the MSL for these two package callouts?
Thank you!
