Holds are not filled in a purely numeric order. They are filled in a way that ensures that customers of a library system get first access to items owned by that library system.  

For example, you may be the seventh person in the queue, but if you are the only RPL customer waiting, and a copy owned by RPL is checked in, you will receive it next. Because of this it is virtually impossible to create an accurate record of where any particular customer is in the queue.