[ekidd]

> Have previous protocols (TCP, UDP, etc) been in widespread use before their respective RFCs?

As other people have noted, yes.

One of the interesting facts about the IETF is that they actually require two existing implementations in order to advance from an RFC to an official "Internet Standard":

The IETF Standards Process (RFC 2026, updated by RFC 6410) requires at least two independent and inter-operable implementations for advancing a protocol specification to Internet Standard.

I suspect that this requirement for two independent implementations that can actually talk to each other is one reason the IETF has a relatively solid track record.

[bonzini]

There are less than 100 Internet Standards (https://www.rfc-editor.org/standards).

[Saint_Genet]

With hindsight, it's kind of funny that 8 of them are about telnet.

[capableweb]

I've been dealing with various things that uses Telnet, mostly "legacy" services that has always used Telnet and there is no reason to switch them. Why is it funny? Telnet is still widely used and has been widely used for a long long time.