I have never owned the earliest versions Charlie (all of my ProVari's have 2.5 trons). But if you are referring to that green one you pictured here a ways back, it is a standard 2.5 IMO.
While not 100%, the different basic Provari versions prior to the P3... Provape-1, Provape-1 V2, Provari V2, Provari V2.5 had differences such as tube diameters and designs, battery sizes, different LED colors, what finishes they were each offered with and in some cases older versions were updated to newer trons for customers if returned to them for the pricey upgrade. Extension caps made them more versatile... a mini 18350 could run an 18490, a standard 18490 could run an 18650. (I bought matchy extension caps for all of mine.)
Very rarely ProVape used an older tube design with newer electronics in it with special finishes for prototypes that they never did a production run of. My 1 of 1 V2 tube/V2.5 tron Coyote Tan Military w/red LED's, black caps, dark screen is an example. There was also a Battleship Gray version of it that I tried to buy but couldn't talk the source out of it for all the tea in China.
The Stealth's and Stealth Mini's were a special project limited edition made for only one specific source who sold them at a much higher price than standard Provari's. He used all the profits to help first response military, police, fire department, EMS, etc folks who were suffering from syndromes associated with those jobs. The Stealth models have a special black triple coat finish that is near bullet proof, a darkened screen with blue LED's for vaping on night ops in stealth mode. The only variation I know of is my 1 of 3 Stealth's that have green LED's instead of blue.
A moldy old picture of five of mine from very early 2014 that shows some of the tube/finish/size differences. L to R, a 2.5 Stealth Mini, 2.5 Stealth, 2.5 w/ext cap, 2x2.5 Military and 2.5 Mini.
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Some resources about the Provari's are still available on line... videos, articles and forum archives. A couple you may want to check out...
The History of ProVape - Guide To Vaping