Decoding Chassis Numbers

[V8 Archie]

I've just been checking out the chassis number on my Chim (making sure I get the right paint code as the body code is not too clear). So having copied it down I thought I'd compare it with this analysis.

seamus said:

First 3 letters are for TVR D = drophead Next 2 characters are type - ie SE Next number is model - ie 4 = 400 P = petrol Next number is random security number Next letter is the build year (A=1980 B = 1981 and so on - i is not used) - build years started in September for the October Motorshow apparently - so you can have a 1990 registered car on a 1991 build year. Next letter is the build month (A=Jan B=Feb and so on - i is not used) Next 3 numbers are believed to be standard/random of no significance.. Final 3 numbers shows the car number - ie 14th car built from the 1991 build year.

Now from this thread I know at least one (old) Chim chassis number starts "SDLDCC4PX" where CC has been interepreted as "Convertible Chariot", but essentially the detail would appear to fit.

Then to my chassis number:
SDL - check.
B - eh?
A0 - why not the same as an older Chim?
3 - umm... does this really mean it's a 450?
R - is this "unleaded petrol" (assuming Q is not used)?
* - this is only just believable as a build year (omitting I, O and Q).
B - but not if this is the month - perhaps J is omitted too.
****** - six digits, check.

Has anyone got any more recent information on how these really work?