There was no limit on who the Gokaigers could become.
There was an episode where 3 of them became Black senshi, and when they quizzed Ninjaman they all became Lion based (With maybe only Marvelous and Don's colors matching their respective color).

Gosei Knight is counted as a silver (well, I assume he is given he was part of the all silver Gokai change) and a sixth ranger. He's not an extra/other hero.

Red - Princess Shinken Red
Blue - Gokai Blue
Yellow - Deka Yellow
Green - Dragon Ranger
Black - Go-on Black
Pink - Time Pink
White - Aba Killer
Silver - Gao Silver
Gold - King Ranger
Disqualified - Gosei Knight

FYI: Gosei Knight is disqualified because it just wouldn't be fair to all the others... He's that awesome!

I count him as one. Unless there's an official list somewhere :eyebrow

What sucks is that they have one, but it left out all 6th senshi :lol

red - change dragon
white - white swan
pink - change phoenix
yellow - yellow mask
blue - change pegasus
black -dyna black
green - dragon ranger

Gokai Silver Gold Mode not good enough?

In fact, Gokaiger lumped him in with the sixths at every given possibility. The first appearance of Basco being another.

I, as in me, as in how I feel and in no official OMG the world'll end! capacity, count him as an other sentai. Lord. Just accept it, and let's move back to get this thread back on topic.

but sentai Gosei Green more classed as a other sentai due to he short apperance where as a gosei knight is more of the 6th ranger of goseiger due to the fact he is the ranger that the earth gave and he has all the cues and colours more of a 6th he would been classed as other if there was more then 6 member ranger in the team.

Gosei Green though was used once in one movie than never mentioned again.