Bill, Two things to keep in mind:
1. 03-A3 production was averaging around 50 or 60 thousand rifles per month so one would expect some extra inventory of barrels but not 8 or 9 months.
2. Modern day serial number lists necessarily have been calculated using the actual number of rifles produced and shipped in a month and applying rules of thumbe regrading scrapped receivers etc.
hope this sheds a little more light.
Regards,
Jim