I have serious doubts that it happened simultaneously though..... so maybe for armies that are a little later then the Perry stuff is aimed at.
Well yes, fashions took time to transfer, if they did at all and there is no way we can put a time frame on something we don't have any evidence for. I personally wouldn't paint figures representing non-Italians with that style of hose, but then again I couldn't honestly say that such a stance is wholly historically accurate with any great degree of certainty.
Italians got about though, we have a whole Ordonnance Company of them in Guelderland in 1477, besides the numbers serving with Duke Charles elsewhere; although whether they'd swapped their native fashion for something more suitable to Northern Europe is worth considering. London, Bordeaux, Bruge and Antwerp were the main ports of call for Italian ships, so the potential for the style to transfer and become common is there at least... I'd put the potential for a new Italian fashion taking off as taking 6 months to a year to make the journey North, rather than years.
As for the Perry figures, I'm no fashion expert by any means, but they represent to me a quite narrow period of time themselves and one that owes more to the 1470's and 80's than it does to 1461 and even more so than 1450, or even 1500. Certainly labelling them as 1450-1500 is a tad anachronistic to say the least. Fashion moved slower than today... but not that slow.