I suspect I am envisioning this situation differently than some posters. OP, can you clarify what the setup was? I am envisioning a casual gathering of 20somethings at a bar that is also open the public with the birthday girl paying for some apps and bringing a cake. I also am envisioning maybe 30-50 people invited, with the expectation that some cannot make it at all, some will be there the whole time, and some will pop in at some point to say happy birthday. I am envisioning a "partying" atmosphere as opposed to a "five year old birthday party" atmosphere (the latter would necessarily be far more structured and involve games and things). I am envisioning a start time of 7, which to me would make an arrival time of 8:30 completely normal, unless the invitation was specific that something special was to happen at a certain time before then. The actual facts make a major difference to me.
TurtleDove: were you there with Lucy, Mary, Tess and me?
You nailed the gathering perfectly, except for the number of guests which were approximately 20. Of these 20 people, 7 were at the dinner. There wasn't anything special happening at a certain time. Being fashionably late was accepted.
Mary could have brought her baby, if she wanted. We were in a private room, no loud music, no smoke and the boy, being a newborn, can't knock things off. The only adult oriented part was the time set: an after dinner event doesn't match very well with infants schedule, I guess!
The party was supposed to last 3 hours, a.k.a. closing time for the bar, and everybody was aware of that.
I'm trying to stay generic, so let's say that dinner time is usually 7:00pm and Lucy invited people for a 8:30pm party. Plenty of time if you eat at home, not so much if you go to the restaurant. Usually restaurant meals last 2+hours (that is perfectly normal and expected). It was highly unlikely that Mary, Tess and the dinner guests would be on time.
Please note that first
Lucy invited people to her birthday and then
Mary and Tess arranged the dinner.