I don't think it's fair for the court to implement a conviction on my name since I never received the letter in the first place...
If you are convicted (whether by way of a guilty plea or having been found guilty following a trial) you will have a criminal conviction recorded against you. The court has no discretion over this.
Have you asked your employer whether a conviction for this offence (which will become "spent" in 12 months) will have any effect?
In any case, from what you've said, I don't believe you are guilty of an offence under s144A:
That’s when the MIB stepped in and sent me a letter saying I didn’t have insurance on ABC123D.
Now, I’ve received the Single Justice Procedure Notice for not having insurance on the old plate, ABC123D,...
But you didn't need to insure a vehicle bearing the reg'n number ABC123D if, for no other reason, (presumably) there was no vehicle bearing that mark.
Section 144 says this:
"For the purposes of this section a vehicle is covered by a policy of insurance if the policy of insurance is in force in relation to the use of the vehicle."Well yours was covered by a policy of insurance because you had a policy which covered its use.
What you may be guilty of is some sort of offence under the legislation covering registration marks, but that's not what you have been charged with.