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DoD troop movements/orders are entirely different than IC stuff. Not to mention, it was already stated that at least some of the documents recovered have been TS/SCI
At the highest levels of classification, there are special rooms you have to use and all sorts of special procedures. 
At lower levels, these might be briefings written specifically for the person who has them, that just happen to include information from a spy or something. So it's very easy for no one to notice classified docs are missing.
Especially for the President or Vice President, so much is classified that I suspect it's pretty easy for things to get lost in the fray. 
I don't blame either person for having classified docs in general, the issue is when they are high-level Top Secret and left unsecured, and especially if you refuse to return them. 
The solution has to be that someone from the archives comes to review every document removed from the White House during a transition of power and signs off before they can leave. That's a lot of work but only every 4-8 years. You have to stop it from happening, ramping up punishments isn't going to do anything. >

It can be a lot less than that. During the Clinton email saga, one of the documents that was labeled classified was a call sheet for the Secretary of State. The classified material was that she was going to call a newly elected African leader to congratulate them. 
Low level classifications are a joke and are treated as a joke. It’s one of the reasons for Director Comey’s famous “no reasonable prosecutor would ever try to prosecute this”.

But a 2012 email released by the State Department appears to challenge that claim because it carries a classified code known as a “portion marking” - and that marking was on the email when it was sent directly to Clinton’s account.
The “C” - which means it was marked classified at the confidential level - is in the left-hand-margin and relates to an April 2012 phone call with Malawi's first female president, Joyce Banda, who took power after the death of President Mutharika in 2012.
"(C)  Purpose of Call: to offer condolences on the passing of President Mukharika and congratulate President Banda on her recent swearing in."

So after that, I’m just not very excited over prosecuting for classified material. It could be someone’s lunch order. They’re not going to tell you. >

It can be even less of a big deal than that. Sometimes publicly known information can be classified. I’m talking about articles in magazines and newspapers. >

My father works for the air force. Someone in his office once got in trouble for forwarding an email using an unsecured emailed address that included a nyt article discussing classified material. Had to retake a classified material training course. Poor bastard. >

I think the issue is (and this could be wrong) is when they are president their homes/offices are secure locations, and so they’re allowed to bring documents with them. It’s when they leave office not all papers are returned, I would assume because there’s so many of them. I’m not sure how the federal government could improve this though, other than having a team of lawyers with security clearances going through the entire personal residence of a president before they leave office, although that feels a tad invasive. >

A SCIF is only required for Above Top Secret classification, properly called TS/SCI. Though it ideally should be used for TS  documents whenever possible, it is not required, particularly in secure facilities, such as one guarded by the Secret Service (VP's residence and office).
Classifications broadly go Confidential -> Secret -> Top Secret -> TS/SCI. Again only SCI (Sensitive Compartmented Information), requires a SCIF (Sensitive Compartmented Information Facility). 
I would also bet money every VP's residence absolutely has a SCIF inside.
That the Archives wasn't tracking any of these documents that were found, ensures they weren't either TS or TS/SCI. So at worst it was something Secret, but most likely it was something Confidential.
Confidential classification can apply to documents retroactively. Potentially you can be handed a non-classified bar napkin, write out a drawing on it about something that you didn't know was true, just suspected - and the napkin will instantly become Classified if it was true. Its a bit Kafkaesque. 
Like if your kid correctly drew the engine schematic of an alien anti gravity engine, their drawing instantly and retroactively becomes TS/SCI. So in the best case scenario, Biden had some documents that became classified after the fact. Like a health record, or his school grades, or his will, etc. It wasn't classified when written, but the moment he became VP or POTUS, those are now property of the Archives, and minor state secrets.
The critical difference with Trump, is that Biden found all these documents himself (his staff), reported them, and handed them over. Whereas Trump was hounded for 2 years by the Archives to give back what wasn't his, and only after his daily refusals to cooperate (unprecedented), was the FBI sent in to raid his residence. >

This is incorrect.  That may be the case for your job, however, I've handled plenty of classified and secret information, and have only once been in a SCIF.  Quite a bit of information distributed out to the rank an file of the military is classified or secret, and that information is not read in a SCIF by the average soldier.