...and that period is essentially two years or the next election which is minimum22 months IIRC.
Sounds right. There is no need or reason to do away with the evidence until it's time to prepare for the next election, at least, and even then the evidence could be preserved at modest cost, for talking purposes if there is an issue still in play.
Ahhh .... 52 USC 20701, and unusual, there actually is a criminal penalty. $1,000 fine or up to a year (not a felony). I don't imagine any prosecutor would bring a case. It's one of those things on the books for looks, just like the laws that prescribe careful oversight of FISA paperwork. There aren't enough hours in a day for the named peeps (AG and FBI Director) to read 1% of that, but on paper they are supposed to personally attest to 100% of it.
Not saying preservation is nutty the same way, just the penalty is merely decoration to make th epublic THINK there is risk to cheating by the government.