Nope, I think they have only ever applied for 100k licenses, due to configurations desired, but the safety certificate permits the numbers I mentioned above, or something like that. I don't really know, this is just stuff I've read online, and the only verification I can find is Wiki. But obviously if you sell 100k tickets, a certain % will always go unused for various reasons.
Technically, at Wembley, it's separated by tiers, and quite difficult for normal ticket holders to move between different tiers once inside. It would be fairly easy to move from say pitch side seats to behind the goals though, as you can move around the concourse of each tier with ease. Whilst they do have stewards on each entrance, they definitely don't / can't check every ticket every time. Pitch standing and the lower tier also share the same concourse at some events, so easy enough to move between these. So much so that at some lesser attended events, such as the Capital FM STB when I attended, at least some of the bottom tier of seats was used as 'unreserved seating' for pitch standing to sit if desired.
Having said all of this, I attended the Euro Semi Final, and there was without a doubt many more than the (covid) restricted number quoted in the press in attendance, many many more. So where there's a will there's a way.