He can no longer pay enough attention to his own missives to remember the sign off.

This is the guy who thinks that knowing what month, day it is, how to read an analog clock, what he had for breakfast 2 days ago, ... is actually an IQ test.

Something like this:

https://www2.gov.bc.ca/assets/gov/health/practitioner-pro/bc-guidelines/cogimp-smmse.pdf

... him passing this is what he is... confusing as an IQ test.