I find the old style WNNN are a different shape between the legs, wider I think than the new style, certainly it seems there's a lot more space in the pocket for stuffing. The tabs on the new style are longer than the old style I think, or maybe it's an illusion but there's three poppers on the old and four on the new. I think the new style look a lot nicer than the old style, higher in the rise and somehow just a lot neater.
I used to get a lot of gaping with both, but now with the old style I fold the insert in 4 instead of three so it's not as wide between the legs and I use a mf cloth instead of the pop-in part, this makes it fit very nicely. With the new style one I use both parts of the insert but I don't popper the small part in I just lay it on top and because DD is a tummy sleeper I fold it to the front which has made it a lot less gapey.
As for absorbency, I think they're about the same tbh, very possibly the old style are a little more absorbent but I'm not 100% on that as I was sold it 2nd hand and the seller pulled a fast one and didn't send the pop-in part of the insert so it's hard to compare fairly.