So... if he said he had done it in 79 but in fact he registered in 1980... this matters to you for some reason?
Your opinion is based on interpretation because his words are ambiguous as I’ve already explained. If you can’t get it, I don’t have a magic wand to wave to make you smarter and a better reader. Sorry.
I’m a retired criminal investigator and have interviewed literally thousands of witnesses in my career. I know how inexact people are in speech and the follow-up questions needed to extract information without leaving anything open to interpretation. Those witness statements may be examined in great detail in court so their exact intent and observations have to be set forth without any gaps, ambiguities or conflicts.
Perhaps he lied or perhaps his advisers pointed out his error to him, assuming there is an error, and he/they decided it wasn’t important enough to make a big deal out of or what they view as a suitable venue to correct it hasn’t presented itself yet.
Or maybe he really did register and made the statement so that a bunch of conspiracy nuts would take the bait. Then he and his media handmaidens can once again ridicule conservatives for once again proving what useful idiots they can be if you just feed them a little BS.