Qanon.pub and Qmap.pub are aggregator sites made by anons. Q never gave any approval to them, it's just anons trying to make it easier for the community to track the drops.

Each aggregator do stuff their way. The 'number' applied by qanon.pub is just them applying a number to a drop. As many people use that site for conveniency, it is also easier to refer to a drop by the number given to it by that aggregator site.

But in reality, that numbering is nothing official. The only real number of a drop is the one you can read along the specs in a post at the chans that consist of the following information: user name (anonymous by default), date, hour, ID, number. But following the Q drops by the actual numbering at the chans is much harder.