Documenting permission to share a patients medical record with other treating physicians is explicitly NOT required by law (called the HIPPAA act). But most places make people fill out forms granting permission to share data with treating providers anyways (because penalties are massive for sharing with non-treating folks).

Somehow people want to shoehorn data transfer and permission slips together into something bitcoin-ish…but the walled garden model is incentivized by the penalties built into the law.