when we are the champions says "when this base scores...."
it doesn't say when A base scores. I believe in the case of this card you have to play it on the base first as your action, and then when that base scores you distribute your counters.
I don't have the card in front of me but based on your wording that is how I would play it.
We Are The Champions- Special: After this base scores, transfer any or all +1 power counters from one of your minions here to another minion.
You can play this as a special after the base that is popping scores.
The text "after this bases scores" refers to the popping base that you're going to play We Are The Champions on and the text "from here" also refers to this base.
It's worded this way to refer to a particular minion on specific base that is relating to another minion which is any minion on another base that will receive those +1 counters as opposed to just putting these counters back into the counter pile.
If it was worded, "Special: After A BASE scores, transfer any or all +1 power counters from one of your minions there to another minion." then that would be a whole other meaning.
The SPECIAL gets played on that popping base which now becomes "this base" and the counters get saved and passed on to another minion.
Remember that SPECIALS are special for a reason!