I wonder whether there exists some general reference on corpus annotation schemes. I looked at two of the main NLP textbooks [1-2], but they don't seem to have any chapter focusing on it. Yet, the annotation scheme can be critical during the annotation phase or downstream when using the annotations for NLP systems.
 Manning, Christopher D., and Hinrich Schütze. Foundations of statistical natural language processing. Vol. 999. Cambridge: MIT press, 1999.
 Martin, James H., and Daniel Jurafsky. "Speech and language processing." International Edition (2000).