> RFCs were originally formalization of what was being used in practice

You may be confusing it with the IETF’s policy.

In early days of the RFCs, most started out as proposals, often but not always with some existing implementation as a jumping-off point to conversation (hence the name). I no longer remember why they started to be numbered and tracked, as the process naturally preceded that.

You can verify what I say by just reading some old ones at the rfc editor site.