maybe simply ask DLT. That way you can be certain.
Like you, I would always be cautious about this type of advice, indeed my licence needs extending next year, but I intend to do it at the end of the 2 years to be certain.
I don't know whether it is a legal requirement, but I would explain that you must have it or you cannot continue, because you must have it for Thai immigration.
They should not refuse to send a photocopy in black and white.
yes, I did the same a few months ago to buy a new car. I don't really see the point of the letter when you have an extension to stay in Thailand for a year, stamped by immigration in your passport, but these are Thai rules and I am happy to comply, to have the privilege to live here. Glad you and your husband got it sorted.