Hi to USA from United Kingdom. Recently imported a 83 Riviera convertible to UK, problem I have is with my local equivalent to your DMV. As our reg year runs August to August and reflects that on our reg plates. My Vin# 1G4AZ67Y6DE413912 decodes all ok except last 6 numbers that will tell you when it was made, can anyone help, or know who might? The body tag is missing from driver door. I love the car but can't get the cherished reg plate for it until I know this info, thanks in advance.

Welcome. I just registered to this forum.
As long as no one else has answered your question, I'll try to help.
The VIN will not reveal when your Riviera was built. The best way to get the date of manufacture is to find the 'cowl' body tag under the hood. It is usually on the driver's (left) side, near the fender. It will have information like the paint codes, model number, etc.
The date code is usually on the lower left of the tag.
It will have a letter/number something like C 05. The letter stands for the week, and the number stands for the month. I could have that reversed, it's been a while since I've looked at one. Anyway, let's say for example your Riv's code is A 06. That would translate to the first week of June, 1983. Or D 10 would be fourth week of October, 1982.
The sequence of production months would go from 08 (August 1982) to 07 (July 1983), roughly.

Hope this helps.

Unfortuately for Riv 83, the date (month & year) info will in fact be on one of the two laminated tags positioned on the driver's side door. It will be the one that also shows gross weight, etc. The other one will give hot/cold tire pressure info, etc. The tag that displays paint color, trim, and other options (RPO data) will be afixed to the inside trunk lid...laminated also. I believe the data tag that was once located inside the hood (rivited to a surface) was stopped in the mid '70's, maybe '74ish?...not sure exactly when.

Dave, the data tag may have been history by 1983, but I know my '78 Grand Am had one, and I'm pretty sure they were used on 1980 models. I hadn't realized they were done away with years ago, but I wouldn't be surprised if they were still in use on the '83 models.
I haven't been looking under hoods in salvage yards as much as I used to.

83, No tags.



stevo