Synthetic documents vs real specimens for training a document detector?

We're collecting a reference holding at Landvex and also planning heavier YOLO training. I'm uneasy about training on anything that looks like a real customer's file, and some official specimen libraries are pretty clearly not meant for reuse in a product.

So… has anyone had luck training primarily on synthetic documents — generated layouts, varied stamps and seals, phone-photo augmentation — and using a small, carefully licensed set of genuine public specimens only for evaluation?

A few things I'm stuck on:

• How close does synthetic need to be before the model just learns the generator?
• Do you still need confirmed forgeries in the training set if the model's job is to find objects, not to classify fake vs real?
• Any practical way to keep provenance on every training image: source, licence, whether it ever contained personal data?

Curious what's actually worked, including the boring failures.