I'm holding out on the possibility of 19/20 eventually being finished; there's still 9 league games to go plus potential Europa/FA cup games. Which could for instance, be the difference between including Bruno Fernandez or Andreas Periera
In answer to your other question, the answer is a little of both. I've used appearance records for each season, but as I said in my OP, I'm not just interested in how many appearances each individual player had, but how frequently the same players played together on the team sheet, in order to get an idea of the
most common "shape" of the side each season.
Take 2010/11 as an example. Rooney and Berbatov have almost an equal amount of starts; by rights, I should keep them both and not even mention Hernandez, who has less starts but more overall appearances when you include him coming off the bench. In addition to that, there's a distinctive shift around February/March during the CL knockouts when after months of Rooney/Berba, you get Rooney/Hernandez and almost never see Berba again. Which is what is represented by the fact that I've gone with Rooney as a constant (though he admittedly also dropped out of the side for a month), and Berba/Hernandez.
In short, it's not an exact science, no.