So are we all doing something wrong when using Perceptol and getting results that do not accord with Ilford's experience when it tested Perceptol and D3200?
I think a lot of people use Delta 3200 for hand held shooting in dark situations, like concerts, or late night street photography. I've done just that, illuminated by just the available ambient light from street lights and buildings, and have been able to cull enough contrast from the film to make them workable in the darkroom. I have either used Rodinal and standing development to get maximum shadow detail out of it, or something like Xtol 1+1 for a very long time, with reduced agitation (say every 3 or 5 minutes).
Using Perceptol for this type of photography is probably not going to work, so I wonder if these are the conditions that Ilford has tested the film in, or if it perhaps is a more normal lighting condition.
If the film instead is tested in daylight conditions, the very flat contrast of Delta 3200 would probably work just fine with something like Perceptol, because there will be less contrast and less deep shadows to fill with detail.
There's too much we don't know about how Ilford has tested the film in order to understand how they got to their results, and to surmise if we're even comparing similar work flows.