When does a 1984 classic car become tax exempt?

I've been offered a Mercedes saloon first registered May 2nd 1984, the owner reckons it'll be tax exempt 7 months from now, but from reading bits and pieces I don't think it'll become tax exempt until...

Can I display an old tax disc on my classic car?

Is it permissible to display an old tax disc on a classic car? I have the complete set of original tax discs since purchasing the car new 36 years ago and would like to display the first one together with...

Is the 40 years tax exemption from the date of manufacture or the date of registration?

After 40 years vehicles are exempt from road fund tax? Is the 40 years from the date of manufacture or the date of registration?

My car was registered in March 1979 - when is it tax free?

My car was registered in March 1979. When is it tax free?