I think that what happens is that some CMs at the assorted hotels go that extra mile and throw in little extras, which could be B&W photos, pins, upgrades, etc. Some of them love doing that kind of thing, and some are all business. It totally depends on the CM and timing -- they are not required to do anything other than check us in and give us the rooms we pay for, but sometimes they want to do certain things for certain guests, for whatever reasons. They can't do extra things for everyone, every day, all the time, so they have to pick and choose. In the morning, perhaps, a room upgrade might not be available. However, 3 hours later maybe a room upgrade is available and someone checks in at just the right time to get one.
I think that sometimes there is a supply of B&W photos in the back (behind the front desk area), and sometimes there isn't. Sometimes the CMs will not give any photos, and sometimes they will give more than one photo. Sometimes they may not give out photos if there are no children in the group. Again, it all depends on the specific CM and the specific day or time of day.
I think the best thing to do is to always just check in without expecting to get anything extra. If it happens, it's a bonus. Of course, if the CMs ask you what you're celebrating then you tell them, but if they don't ask and you try too hard to remind them that you're celebrating something, that could work against you. I think they will actually resist the people who try too hard to get something.