In 1978, it was my first year in the Air Force, and I registered to vote while overseas. I actually sent the paperwork into the state twelve weeks prior to the election. The ballot? It arrived six days prior to the election. I turned it around that day and mailed it out (via military postal in Germany). Over the next twenty years, I voted continually the same way.
At some point, while visiting the home-state after retirement....I talked to the county clerk and she kinda admitted that they tended to not count the absentee votes that arrived after the voting day....if they arrived prior to that, it was virtually guaranteed to be counted. Since that point (about five years ago), my state now emails you a pin number and gives you a seven-day period (all prior to the election) to vote on-line.
I suspect if you go state by state....more than forty of the states are broken in respect to absentee ballots. Either people are getting the ballots who shouldn’t vote, or they just don’t count them because they are mailed out late and can’t return on time. But behind all of this....the voting officials just don’t care. This has all become a Frankenstein-like system and it’s built to be corrupted.
Your 1978 experience parallels mine in that same time frame and also in Germany. Even worse, one of my “extra duties” as a young lieutenant in that time/place was Unit Voting Officer. I was trying to help all the soldiers in the unit and even I couldn’t get the system to work. Your info about the PIN and online voting seems the best technology solution.