I have doubts that TA and Stronglight tapers are really ISO. ISO (the organisation) dates from 1947, and the square taper standard has date 1991. Does anyone know when that standard was first published? I don't.

Sutherland has amassed a lot of measurement information on spindles, and it goes like this: from small taper end to large, they list Ofmega, Zeus, ISO, Campy** and JIS (6th ed, p.2-5). Then, next page, they observe that
"TA cranks: crank bolt face comes close to flush with the ends of many spindles." (including Campagnolo?)
"Strongllght, JiS (Japan Industry Standards), and Suglno AT cranks: bottom on the ends of the flat on most spindles except Stronglight, TA, JIS, and Phil Wood." (does most include Campagnolo?)
and finally
"JIS spindles can be used to place chain line farther from the frame with Stronglight or TA cranks."

From this I infer (perhaps wrongly) that TA + Stronglight are both in the JIS-range (stubbier than Campy?, which they say is stubbier than ISO), and that TA spindles may have been a bit less stubby than Stronglight.

But what I take from this is that if you don't have a Stronglight or TA spindle for your Pro 5 vis or vintage Stronglight crank (there; now I'm on topic), you can probably use JIS without any problem, maybe subtracting a couple/few mm unless the sockets are worn.

Footnote:
**in 1992 or thereabouts, Campagnolo changed to ISO from their "proprietary" standard (that's supposedly stubbier than ISO) -- which proprietary taper was emulated for spindles/sockets on other vintage "racing-oriented" equipment like Sugino Mighty (*), SunTour Superbe (made by Sugino for SunTour) and, I think, even Dura-Ace in some earlier years. Phil Wood never made "Campy" tapers, but recommended JIS tapers for those who wanted Phil BB for a Campy crank.