It had variable length addressing "up to 20 bytes", which IIRC was done so that it could easily accommodate different addressing systems into one. Unfortunately

It had variable length addressing "up to 20 bytes", which IIRC was done so that it could easily accommodate different addressing systems into one. Unfortunately, variable length fields make for really annoying hardware implementations. TUBA (replacement of IP with CLNP, running TCP and UDP on top) mandated use of max size addresses always, to make it simpler to decode, as part of "Internet Profile CLNP".