Dumb question on erlang ports

[John Parkey]

Hi

Sorry to bother you, but I am coming back to doing some erlang dev work on
freebsd, after a while away.

I am a bit confused by there being erlang-runtime ports for versions 20 and
21, but the main erlang lang port is at version 19.3.  Presumably version
19.3 cannot be used to develop stuff which runs on 21?  If not, what is the
rationale for the existence of the later runtimes?

Thanks for your help

John