The operation of the driver testing service is the responsibility of the Road Safety Authority, and I have no role in individual cases.
I have received the same correspondence from the individual in question, and am replying directly.
While I cannot comment on individual cases, the legal issues are as follows. The Licensing of Drivers Regulations define design gross vehicle weight as "the gross weight of the vehicle laden with the heaviest load which it can reasonably carry having regard to the engine capacity, brakes, tyres and general construction of the vehicle." The RSA is therefore correct in referring to the laden rather than unladen weight.
In regard to the amnesty issue, driver licensing law was changed in 1989. Before then, one category covered driving a car and driving a car plus trailer. After that, the two were split. People with a licence before that date were entitled to claim both new categories when renewing their licence. Inadvertently but understandably, many did not, and so lost their entitlement to a trailer.
Last year, in response to representations from farming organisations, I agreed to allow those licence holders who held a full licence for car and car plus trailer before the change in 1989, and had inadvertently lost it to reclaim it. The Road Safety Authority set out a time period in late last year within which drivers who could prove that they had held a full licence pre-1989 could reclaim their trailer entitlement. This was a once-off opportunity to reclaim the licence.