International transfer sounds like a legal category. In practice it is an infrastructure fact: a region in a console, a CDN edge, a support tool with a US-hosted inbox. The paperwork is downstream of a decision an engineer made in a dropdown.
Where transfers hide
They are rarely in the database. They are in the analytics pipeline, the error tracker, the transactional e-mail provider, the AI API and the support desk, tools chosen for speed, each with its own default region.
Map it from the outside
You can reconstruct most of your own transfer map in an afternoon without touching a single system:
Then write it down once, properly
For each transfer, the record needs the destination country, the mechanism you rely on, the categories of data and the purpose. A record that exists is worth more than a perfect record that does not.
Keep it beside the vendor list rather than inside a document, so that adding a vendor is what updates the map.
See the vendors and regions your site reveals.
The free assessment lists every third-party host your pages contact and where each one resolves, a first draft of your transfer map, from the outside.