I started an RMA for my 1TB OLED Limited Edition on Sunday for a stuck/dead pixel but didn’t include a picture.
Valve got back to me and asked for one, and now I’m waiting for them to get back to me again.
Save yourself some time, include a picture of the problem when submitting an RMA.
It is actually unusual for them not to accept the RMA without proof. They normally accept them then just charge for return postage if the problem isn’t confirmed on their end.