If someone proposes some dates to get together, and you tell them you're free on those dates, are you supposed to keep those dates free until they pick one?

The leader of an organization that my daughter belongs to (a scouting organization for females) proposed two possible dates for a meeting. The group is small, and the moms responded with which of those dates are best for them. The majority picked a Thursday. My daughter was available on both dates and I responded as such. About a week later, the leader of the group emailed with the definitive meeting date. At that point, we (my daughter and I) were no longer available on that date, and another girl was not either. The other mom responded that her daughter was no longer available and I did, as well.

One of the moms responded with an email pointing out that two of the girls were now not available, and the leader sent an email that had an annoyed tone. I won’t convey the details – it was not rude but her wording indicated that she was annoyed that we were no longer available. The wording was how a lot of effort goes into scheduling the meetings and how everyone had been available on the date she chose. I responded with an apologetic email.

My feelings were (and are) that if something is not definite, and something else comes along, we are free and it’s “first come, first served.”

What do you think? Would you hold dates open until a decision is made, or would you consider the dates free for other things, because a decision hasn’t been made?