In our prairies, we are pretty subjective during the first several years. We rarely visit the sites during the first year or two because the early establishment is so variable from year to year that it can be more frustrating than productive to go look at them. We generally trust that good things are happening or will happen. If I do go look, I'll get down on hands and knees and see if I can find a native grass seedling and forb seedling within a few feet of where I'm sitting. If I do, I'm ecstatic. If I don't, I don't worry too much about it... By about year three, we expect to see native grass plants every square meter or so, and at least a couple native forbs in the same area. That's pretty easy to check by just walking through it. sorry not to be more quantitative, but based on years of experience (and conversations with other practitioners) it doesn't seem worthwhile to worry too much in those first couple years.