S&S customers are included in your repeat purchase customer data.

However we are unable to break out S&S customers from non-S&S customers by default. This is because Amazon does not provide the data to us in an automated way (i.e. via an API) so the only way to acquire the data is to login to Seller Central and manually download the data.

We are able to to do this as part of a custom (paid) project so if this is of interest, please reach out to us.

We regularly ask Amazon when the S&S data will be available via the API. Rest assured we'll make it a top priority when it is!