The name is a possible reference to 420, a slang for marijuana.

Another is that each entry has the earliest possible printed reference from history.

The term is the most offensive possible reference to a person of Chinese descent.

He seemed to be taking in everything and then mentally filing it away for possible future reference.

Three possible early references to Movses in other sources are usually identified.

This is a possible reference to the cat from the science fiction film Alien.

Where possible references are given to printed or online reproductions.

Nothing earth-shattering, but something to keep in mind for future possible reference.

Grimly, he filed the smell away, for possible future reference.

The outline gives all possible references I have found within the parameters you set.