Sure. Exactly what numbers would you like? I obviously don't have precise numbers for every school, but some schools like Pitt and Vanderbilt publicly announced last year that they were increasing the number of IIs due to the huge increase in applicants. Applications dropped back this year, and so did the number of IIs. You can go on school specific threads earlier this cycle and see the discussions yourself.
As for the rest of your analysis, I will respond step by step and point out what you are missing.
1. Increase in apps making IIs harder to get. True, even with more IIs going out last year at some schools.
2. Increased ease of interviewing -> more people attending II's, Possible. Anecdotally people reported taking IIs tey would have turned down in the past, but this did not manifest in schools having massive drops in yield because they same people were grabbing IIs all over the country and not letting go.
3. Less people getting II's + More people attending II's -> fewer individual people holding multiple acceptances. NO! This is the fatal flaw in your analysis. The massive increase in apps making it harder to actually get an II did NOT mean less people received IIs. In fact, more people did, as some schools ramped up. But no school actually decreased the number of IIs.
Look at it like this -- the number of seats remained constant at around 22K. If fewer people were holding multiple As, that could only mean MORE people had a single A, since the number of As does not change. If WL movement did actually go down, that would only be because it was easier to get an initial A than in the past.
It didn't really happen. Every year, people look for a surge in WL movement. It never seems to come, like Linus waiting for the Great Pumpkin. The movement is pretty constant from year to year. Individual schools have wild swings, but, collectively, the movement doesn't vary a lot from year to year. Just go back and look at the SDN WL threads from the past 2 or 3 years.
As you specifically, you have nothing to justify. Last year was by far the most brutal in recent memory. 4 WLs made you statistically likely to receive 1 A, but, that was far from a guarantee and is highly dependent on just which schools you are waiting for. How are you doing this time around?