My understanding is that, as well as being a penetrating lubricant, real Plus Gas Formula A is able to draw out the included water from rust reducing its volume and hence the sticktion between a rusted in bolt and its nut or rusted shaft and its housing. Which obviously makes things easier to turn or move.
A pure penetrating oil merely lubricates the various surfaces, whether between rust and component or between prust particles to ease movement.
I have in the past seen several applications of Plus Gas A reduce the binding of a rusted in shaft from immobile with a hammer to stiff hand pull out levels so I'm inclined to believe the claims. But it does need time to work. Overnight is good.
WD40 is always to hand and gets used more than it should for all sorts of things despite being pretty crap at everything compared to the job specific special sauces.
Clive