Very few people test their compost to determine what nutrients are in their compost, and what percentages is there. Some of the absolute best compost has a small percentage of just 3 nutrients a plant needs. They still need 10 more.

A problem with unfinished compost, in addition to those nutrients not being available to the plant, is any weed seeds or plant disease in that compost didn't reach the needed temperatures to kill it. When adding unfinished compost to the garden you risk introducing weeds and disease back to the garden.