Training a model on an EHR is worse than nothing. Epic allows infinite customization, and customers build up their own informal standards such that you can’t dump and compare data across multiple sites.
While it's not easy or simple for every facility, in general it seems to be possible to pull whatever data you want from Epic and other EHRs. There might be a fee, work order, and vendor involved, but if you want a 100GB CSV containing certain columns, it's generally possible.
Of course matching that data up with sets from other locations will still involve someone in the middle gluing it all together.
Of course matching that data up with sets from other locations will still involve someone in the middle gluing it all together.