To me “open letter” usually signifies that there are a significant number of signatories, like various open letters to governments from the scientific community

To me “open letter” usually signifies that there are a significant number of signatories, like various open letters to governments from the scientific community, with one not being a significant enough number to qualify however important that one person is (or thinks they are!). Sort-of like difference between some random person telling you that you are too drunk too often, and a group of concerned friends & relatives staging an intervention, to put it into a social context. It is that significant number of significant (either to the receiver of the letter, to the public at large, or both) people that makes it important. Here I feel the term is being used incorrectly.