Fair play to you for posting that, took a lot of effort I imagine and has been a topic I've been surprised not to find more information on in the past, so good to read.It wasn't remotely thorough or sophisticated. They were identified based on whoever came to mind as either big transfers, big takeovers or big financial meltdowns really and then cross-referencing with Wikipedia for results and Transfermarkt for player incomings. It will no doubt make me look even sadder, but probably about 90 minutes of work all in. I'm a researcher by trade though, so it's not much effort.
How did you identify clubs who had signed 6+ players, or clubs who had lost a key striker - your own knowledge, or is there some kind of database you're working from?
Also, did you look at what happens when you sign 6+ players AND lose your key striker? I imagine the n size is too small for meaningful comparison. But that's the situation we're in.
With the exception of a couple of teams (United with Ronaldo, Arsenal with Adebayor and van Persie), the teams that lost a big player all brought in 6+ players so whatever the numbers I said up there are pretty much what they are.
I think what I'd take away from that mainly is the trend to having a poorer goal difference (which I think you can take as a surrogate for cohesion) if you sign more players. Small n, but I suspect that trend would hold up.