That point make no sense, wathever if the product is there for 9 month, this best seller list is updated hourly, this is the sale for the last hour.
Company A and Company B are direct competitors.
Company A has four products available at any given time that change every year.
Company B has twelve products available at any given time that change every three months.
Assume company B sells twice the number of total products as company A.
Assume the total products sold are distributed evenly among all the products available.
We are looking for the most number of sells for one unique product at given time intervals.
1 Mo ---- Company A = X ---- Company B = 2/3 X
6 Mo ---- Company A = 6X ---- Company B = 2 X
12 Mo ---- Company A = 12X ---- Company B = 2 X
Obviously this is a very simple example with some simple assumptions but you should get the idea. Even with a short sample period and half the total sells, the company with 1/3 fewer unique products sells more of each individual item than does the company with more items.