The late, great David Vestal used to be a stickler for terminology, ...
There are two scenarios. One is where the entire print is exposed to a very hard and a very soft filter, no burning or dodging. Vestal, Howard Bond and others have tested and concluded that there is no difference between a print made this way and a print made by a single filter.
The second scenario is where one filter is used for the main exposure and then a different filter is used for the sky or foreground. This has obvious benefits and produces results not able to be obtained with a single filter. So, in the interests of clarity, I would like to see different words used to describe the two scenarios.
How about split grade for the first, and multi grade for the second?
I was taught “split grade” by one of the best: Les McLean. Even then, I thought it was an interesting technique that would be useful IF I could not determine the correct single contrast for a negative. At the same workshop, Les also demonstrated the (then) fairly new RHDesigns Stopclock timer. I did not need a new (and expensive) timer at the time, but shortly thereafter, my enlarger timer died. So, I splurged and bought a Stopclock. (Really glad I did, because of “F-stop” timing, but that’s another story …)
One of the first things I discovered, was that after doing the two separate test strips for the hard and soft split times, and programing them into the Stopclock, the timer could then tell you the single grade that was the equivalent! It took very little research, and only a few prints of my own, to discover what Mark, Vestal, Bond, et al, are saying.
“Multi grade” technique obviously has its uses. Split grade, i.e., simply separating the hard and soft exposures, has uses, as well, but DOES NOT magically yield better prints in and of itself.
I’ve also seen a number of videos and webpages “teaching” split grade, where this is taken to an odd extreme. One makes a test strip at grade 2 or 2.5. Then takes that time and halves it between 0 and 5! This is extra work and makes no sense at all. (IMHO)