I have not read the article yet as I am in the US and it takes a little bit to get here but I am a little confused here. Is the article talking about split filter printing or using two developers to control the contrast of graded papers? If we are talking about split filter printing then the developers really don't come into play as I see it.
I believe you're correct. As a long-time practitioner of both split filter and divided development, the two techniques are separate, though obviously related in one's own practice. Your choice of developers, for example, will influence the contrast you build into the print under the enlarger, but there's no necessary connection between the two.
I have used a lot of print developers with this technique. Now if the author is writing about controlling the contrast via different developers then the way I have done it is to use a soft working developer (like Selectol Soft) and regular working developer (like Dektol). The print is partially developed in the Selectol Soft for a portion of the time and then in the Dektol for the remainder of the time. I am not sure this technique would be of any benefit with variable contrast papers.
A more effective (IMHO) method of divided development for contrast control is NOT to use a full one-solution developer like Dektol in one tray and another full one-solution developer like Selectol in a second. Rather, divide the developer itself into two solutions--developing agents (Metol, Phenidone, HQ, ascorbic acid, whatever) ONLY in Bath #1. In Bath #2, ONLY activator (plain carbonate is fine). If you have room in your sink, make up two Bath #1's--one with a "harder" developer formula (mixed as above) like D-72 (Dektol) and one with a "softer" formula (like Selectol). Then, depending on the effect you want, use EITHER the soft developer OR the hard Developer for a given print, BUT NOT BOTH. Then on to Bath 2 (the activator).
With this method, the print needs to be in Bath A no longer than about 20 seconds, but even if you leave it in for three minutes, no image will appear. Also no temperature controls are necessary. By separating developing agents from activator, you effectively eliminate time/temp considerations.
In Bath B, the image appears very rapidly (or more slowly if your solution is quite cold, e.g. 50-60 F.) and develops to completion, but no further. You can leave it in all day, but it won't get darker. Only the amount of agents soaked up in Bath B can be activated. It is possible to pull it too soon and end up with weak blacks. I usually find that at room temp, Bath B takes about 45 seconds or so to get to completion. As the carbonate becomes exhausted, it may take a few seconds longer.
Another advantage to this technique is that you can keep re-using Bath A over and over again, because it doesn't become contaminated or exhausted. It just gets physically used up as a certain amount is absorbed by the paper stock. I mix it a half gallon at a time and usually don't have to mix any more for about six months. Just pour it back into the jug when finished. Bath B does become exhausted, and I mix a fresh tray for each darkroom session, the lazy man's way--pour a half gallon of water into the tray, throw in 1/2 cup of Arm & Hammer Washing Soda or pH Plus (carbonate), and rock the tray a few times to agitate. Then, while I'm setting up the rest of my trays, selecting my negs, etc., the carbonate dissolves, so that by the time I'm ready to print, Bath B is ready too.
With graded papers, the use of EITHER a soft OR a hard Bath A will give you intermediate grades. I.E., a #2 paper run through the soft Bath A will result in a print with about a 1 1/2 grade contrast. Run through a hard Bath A, it will result in a 2 1/2 grade contrast.
It works perfectly well with variable contrast papers too, which is what I use exclusively now. With variable contrast, the split filter printing and true divided developer technique I've described, make getting excellent work prints on the first try almost sinfully easy.
Larry