I'm in a hobby group with 9 other people. One of these people offered to have us round for a gathering but has been chopping and changing dates for a while. She finally told us it would be this weekend.
So I followed up to ask if this was still the case, she says 'yes definitely this week' and I responded great, I wanted to know so I could get back to other friends about some Christmas drinks but I'd keep that day free. All good, I did that and made my other plans.
A day or 2 later in the group chat a mutual friend asks to postpone by a week so they could attend and the friend replied 'that should be ok, i'm flexible' and has essentially said it will be in a weeks time now which I and another person can't make!
YABU - the friend was right to throw it out there to the group/can't please everyone
YANBU - she should have kept her word