Lomcovaks
1974 is before the Customs & Excise amnesty.
This has never actually happened to me personally but I have heard that somebody who buys a "VAT paid" (which means that at some time it has been owned by a NON VAT-registered person or corporate body) plane here in the UK, and doesn't get evidence that VAT has been paid on it, and cannot obtain that evidence afterwards, he's got big potential trouble...
This requirement for VAT docs tends to feature prominently on checklists for buying used planes.
Over the years, many planes have been imported simply by having been flown over to the UK, which anybody can do anytime without any checks. When it was later moved to G-reg, the CAA would not check with C&E if VAT has been paid. The C&E amnesty took care of the oldest ones only.