Nope, no formula change, just the propellant.
Testors Dullcote will go satin or even gloss for a number of reason mostly down to its carrier (nitrocellulose) which is naturally shiny.
If you dont shake the can well enough, spray too closely or spray too much, then you wont get a matte finish, the more you spray, the more closely and the ehvier, the worse it will get.
Dullcote is a lacquer (not a varnish) that is VERY dependent on being used with VERY fine mistings, rather than direct spraying. Your model should be placed at a point where the spray/mist gently falls on to it, you should not be spraying with any force, on to the model - otherwise it will go satin.
Army Painter Matt is OK, but very granular (in the extreeme), temperature sensitive and tends to white-out...but then so is every other aerosol out there.
I've got both, sell both, so i'm not really picking a favourite: but my personal experience is that Testors Dullcote is the most relaible, most matte but probably the most difficult to perfect the technique of using. Army painter is reaosnably Matte, but futt-bugly at times as the matting agent (grain) is so large you can actually see it. It is, like the coloured primers, exceptionally thick, which you may or may not like; i love the primer colours but am really going off the thickness of the paint.
However: no changes to Testors' formula and its just as matte as it always was. It is, in all honesty, just down to application and preperation (warm, shaken and misted).