I have an 11A build LOS Camaro Coupe that has A638 in that position. I was told on here about the Body Scheduling code. It was only used on LOS cars, the letter was used to indicate the build day of the month; A was 1 st., B was 2nd., C - 3 rd., etc., etc. So - I - would have been the 9 th. build day of Nov.. The letter was supposed to revert back to A on the 1 st. build day of every month, I was told this did not always happen as planned.