Get a list of all active users using classic reports?

With Qualtrics soon deprecating classic reports, our communications dept wants to send a message to all users that have Classic Reports (I know Qualtrics is doing this, but hey, I don't make the requests).

I can get a list of all users in my organization by sending a get to  "https://ca1.qualtrics.com/API/v3/users/"
I can do things like check if a user has API enabled by sending a get to the specific user and checking
-------- if response.json()['result']['permissions']['controlPanel']['accountPermissions']['accessApi']['calculatedState'] == "on":

But that's a discrete thing - API on vs API off.
Does anyone have any idea how to check if the user's using classic reports? It's hard because that's so encompassing - maybe they have a public report, but maybe that's just something they use themselves, and so they haven't customized it at all and just look at the Reports tab every so often.
Any and all ideas welcome, thanks!