Roman Standards

[Bryan]

I don't seem to see where Pliny is mentioning about the five different standards being between different legions, he clearly is referring to different ranks/divisions of troops when he mentions that all but the eagle standards were left back in camp before battle.
And wasn't the customary number of consular legions drawn every year four not five?

If they were meant for four ranks then Velite, Hastati, Principes, triari all get one each. Who gets the fifth? Speculation is fine, looking for ideas of how this could make sense.