I was upstairs in the guestroom at Katie's house in Pulborough. There was sunlight through rain and looking at the window was just a glare, but projected on the wall was this bit of information:
The two bottom panes had a curtain over them, so those would need to have that moved to check, but the two top panes that seemed the same looking out that day are very different. The one on the left in the shadow/projection is newer glass. So at some point, that pane was broken and replaced. The other is old glass, settling into flowy patterns. I'm sure that in different light, if one had something to focus on through the glass, it would have been noticeable by looking. The windows in the front room, looking out at trees and flowers, showed their waviness. But maybe these windows, only seeing clouds and sky, are not usually obviously different.
At Hampton court, there were dozens of windows, each with a dozen or sixteen or some panes of glass, most of them obviously old glass. Public bathrooms had been build into some of those rooms, and the windows (which went to the courtyard outside, and were up high, had new glass. So I figured any old glass remaining in those now-toilet-facilities windows had been put into the nicer, more museum-purposed rooms.