Understanding Society User Support

I have merged whhresp and windresp files using a m:1 match as you mentioned before. However, when matching pid between waves J and O I have found that only 1500 individuals are included in both waves. I am under the impression that this should not be the case as all individuals in the sample are followed for every wave? So should all individuals interviewed in wave J also have been interviewed in wave O? Please could you let me know if this is the case and possibly what could have led me to only finding 1500 persons with the same pids across waves J and O.

Thank you