Mossberg 600
I've only just discovered your enquiry about a Mossberg 600, I own a Mossberg 600 AT pump action model with C-lect choke. This was purchased new by me in September 1981 in the UK. The serial No. on mine is designated beginning with the letter H, logically this would make your gun a little older than mine but no way of telling by how much,
I still have the original instruction/booklet manual (now a little crumpled) showing correct assembly/dis-assembly and how to maintain it etc. Hope this information is not too late and that it may be of some value to your query, perhaps Mossberg could give you more detailed information as to the exact date of manufacture.
Regards
bobbydee
