Know that the L3H grades are not the be all end all because the maximums are unlimited (of course other than reversal for EBI/HALO). Where grades become a "thing" is if you need to special order unfilmed tubes and have a minimum spec requirement. This is more common with sellers who only order unfilmed tubes as needed. If a customer has a certain minimum spec request well then they have to order accordingly.
If you're shopping for a new device with unfilmed tubes, at TNVC we offer specs requests for no additional charge, and we'll gladly make recommendations to help you decide. We use 18UM's on our own custom contract and if you follow some of the threads you will see that the specs commonly exceed the other grades. This is because we receive A LOT of tubes. I know guys who special ordered higher grades (and paid more for it *not from us*) and received what most people nowadays would consider average-to-below average specs.
Ironically, some of the people who lecture about not "buying into" high specs vs lower, unfilmed vs filmed, etc. etc. will shout from the roof tops when they have higher unfilmed grades for sale such as 24's, lol.