They will try to accommodate everything but there is a higher risk of items not travelling if there is no advance notification and they are unable to accommodate everything. For example, some years back, the number of cycles that were checked in and were unnotified, were too many to be accommodated. As this was only picked up once the cycles were checked in. It was too late to do anything and some were left behind. Turns out there was a cycling event and not one that would normally be booked by groups such as Team GB, but by lots of individuals so there was no advance notification. There was then a scramble to try to put A321s onto the next outlet flight to ship items that were left and plan or anything that could be checked in over the coming days.