Yes, it is possible to join the AID after the 16th of August. If so, please remark this when you sign up for the AID at www.aidwageningen.nl. The last day on which you can still join the AID is on Monday, August 19.
If you are not able to start the AID on the 16th of August or if you start later than 12:00 hours you can register in the Forum building (Droevendaalsesteeg 2) in room C103. There is the temporary AID office. If you register you will get your AID bag, AID goodies (if you ordered it) and your wristband. Your AID wristband will grant you entrance to the different AID program parts. Without a wristband you will not have access to the AID program. Therefore it is really important that you register as soon as possible! The AID office is opened from early in the morning till late in the evening.