Let me give you an example. If I were writing an article on a drug and I included the sentence "tyrosine is an amino acid", I would be expressing a relation that is learnt in secondary education. It being an amino acid is the first thing anyone would learn about tyrosine. Is this reference worthy?
There is no such thing as over-referencing. There is no such thing as "common knowledge" regarding encyclopedic content. If it feels "common knowledge", it may be lacking relevancy at least in a certain context.
Mathias