But the agreements themselves are completely informal and an overview of what the US expects to see happen in order to maintain the tariff reductions. The interpretation of whether the other country or group of countries is abiding the agreement is entirely at the discretion of Trump.

So there's no such thing as a loop hole. If Trump isn't satisfied with e.g. the EU's progress towards implementing said agreement, he can increase tariffs back to where they were at his discretion, with or without reason given. So there's no such thing as a loop hole in this sort of agreement.

Just curious, how would this help with anything, other than documentation purposes?

$500 billion for Stargate!

How many of Trump's investment deals from the first term panned out?

Like the president deciding exactly where business investment should be made is the definition of a government command economy (remember that "Communism" bogeyman???), which used to be the antithesis of American economic policy (at least in theory), and now we're just all like "OK, cool". It's so sickening.