Why not ask the source? I think there might be standards within the lumber industry. I think members adhere. For me the only time the rough wood ends up too thin is when it is crooked and takes a lot of work on the jointer and planer to flatten it.
I would design and plan with a confidence level... If you buy a 12/4 board there's a best guess as to what thickness you're going to get out of it... Something like this:
2.25" thick = 100% confidence
2.5" thick = 90% confidence
2.75" thick = 60% confidence
2.9" thick = 25% confidence