Huh? You mean an ampersand? #/& were the original channel prefixes. The plus channel prefix (which means an unmoderated channel) did not come till later. Even then & prefixes have a different connotation from # channel prefix.

Seems like there were + prefixes before - https://www.alien.net.au/irc/chantypes.html

I can't remember exactly where I first encountered the plus prefix (it's been a long time), but I remember # and + more than &.

Huh? That says the + prefix came from RFC2811 which came out in 2000. So after RFC 1459 which only specifies &/# as channel prefixes.