You googled this and copied from the first result that showed up. Which is from the county council in Tipperary
If you don't mind I'll stick to the premise (until proven wrong) that it is based on the first date of registration (which is easily proven as all cars in this country have an official first date of registration) and not the date of manufacture, which is a far more vague concept, not in the last place because it happened in another jurisdiction as Ireland doesn't manufacture or hasn't manufactured a lot of cars. This forum's charger has said for many years that vintage tax is based on first date of registration. NCT is also based on first date of registration
And are you seriously saying date of manufacture is a more vague concept than date of registration? A car can be re-registered in various jurisdictions, it can only be manufactured once. My CRX has a first registration date of 1996 on the V5, will have a first date in Ireland of 2020 - but its a 1989 car. Its literally impossible to provide the first date of registration in Japan - so not exactly as 'easy to prove' as you say. Anyway, I've actually done it - multiple times - I've phoned the tax office to discuss it when I had queries on it. And I know plenty of others who have done the exact same.
Last thread on Backroads recently -
Well credit and acknowledgement to the nice lady in the local motor tax office.
This car has a 1990 plate, came from the UK to Ireland in 1996, and the VLC shows the first reg date as 10/09/1990.
But I'd established it's exact build date as being in May of 1990 using a few VIN lookup tools which all returned the same date.
But none of that needed to even be mentioned. The boss man simply phoned the motor tax office to enquire about switching the car to vintage tax, the nice lady who took the call sent out the necessary forms and they were swiftly sent back fully completed. 4 working days later the new tax disc arrived and the vehicle is now officially registered as vintage.
No need for any VIN reports or to approach Mercedes for a letter.
Always nice to have a positive and hassle free experience with a govt or council dept.