A great game to play took many hours had lots of fun.
Toll Station (card #99)
1$ M.C./ 1 titanium
(Increase your M.C. production 1 step for each space tag your OPPONENTS have)
My question - Are the used events cards that are kept by the players, count towards the space tags?
Tags on played event cards only count at the time you play them, not at any other time.
This can modify how you pay for them, or how much, and can trigger other cards.
However, events are then turned down, and their tags do not count from this point on.
Not for effects on other cards (such as Toll Station), and not for the science award at the end of the game either.
I am not sure why you underlined the word 'used'.
All cards only refer to cards in play (you can't see cards in hand anyway)