Part of it could even be difference in friends on Facebook.
For my sixteenth birthday, I had a big party. Everyone brought cameras and posted them. The problem was that at the time, I'd invited people from several social circles, and depending on the privacy settings of each, that meant half the guests from the party wouldn't be able to see some of the pictures, and that they couldn't be tagged in them, ect.
A lot of people kept asking what had happened to *all* the pictures from my party, because they'd seen about thirty cameras floating around the area and knew that there had to be more. So in the end, I had to combine everyone's albums into one big one and put it on my facebook. This way, even with the people that I was the only common friend, (which there were a lot of, a bunch of my friends came in from outside the city to come to my party.) everyone got the chance to see, tag themselves, comment, or decide to make it their profile picture. In the description of the album, I put, "Taken by... everyone. Too many to name! :^D" and some people went on and commented the pictures they took and said, "Hey! I took that one, hehehe!" or something along those lines.
Although, I'm going to be frank here... I'm not entirely sure there *is* such a thing as "facebook etiquette". Everyone kind of does what they want, and as long as it doesn't involve straight out harassment, pictures that can be reported, or threats made, there really isn't any kind of rules.