My recollection of how they were played differs slightly from what I'm reading in the Rulebook, but, the rules are this:

You can include a Battlefield Condition when you assemble your force.
After starting areas have been determined, both players reveal their BFCs.
Apply the BFC rules as applicable.
A Theme Team may choose to cancel one BFC condition when the BFCs are revealed.

What I recall that no longer seems to be in print or clearly stated:
You were able to include a number of BFCs equal to the number of rounds played.
You could only play one BFC per round.
You could not have multiple copies of the same BFC.
The Theme Team cancellation effect could be used only once during the tournament.

Perhaps someone else has a better recollection of this than me.

What y'all are remembering is from the comprehensive tournament rules document (May 2, 2013 edition)

2.3.1

Battlefield Condition Cards:
A player is not required to bring any battlefield condition cards
(BFC) to an event, but they are legal in all Golden Age events. Each player can add a number of BFCs to his or her force equal to the total number of rounds in the tournament (counting both Swiss and elimination rounds). Players must decide which BFCs to add to their forces before the first round of the tournament begins or the judge requires a written
list, whichever comes first. None of the BFCs on your force can share the same name, regardless of any other differences in set symbol or other markings.

After choosing starting areas (see Battlefield Conditions
on page 21 of the HeroClix 2011 Core Rulebook), each player chooses a BFC to use for that match from the BFCs selected earlier in the tournament. All players reveal their card at the same time. Players can choose to reveal no card (players can use placeholder cards – any card
-sized element except another BFC – to reveal as “no card”). Players can’t change their choice once another player has revealed their selection.

At the end of the round in which a BFC has been revealed, that BFC is removed from the tournament and can’t be selected in future rounds. Written notation should be made by the judge or opponent at the judge’s discretion as to which BFC was played in each round. For tournaments both with and without force lists, you must show your opponent(s) which
BFCs are available to you to reveal if requested before anyone reveals a BFC for the round.

This reads to me as "Don't even bother trying to use them"