Barrel Stamp Below the Date

I know I have read this before, but I cannot find the thread...What does an "A" stamped below the date on a 10-19 SA barrel indicate ?
Thanks

I believe it means that the barrel was salvaged from an earlier rifle and was considered "acceptable" for continued use.

When the rifle was returned for overhaul, the barrel was judged ok to use, so was not replaced, but rather remained with the receiver.