Order Weeks Since Onsale: for a subscription dashboard.

Hi friends,

When I use Order Weeks Since Onsale on the x-axis of a chart to compare subscriptions from previous season, what date is it looking to for that on sale date? 

The answer to that may fix my second question, which is- in the graph I've attached, I know I've had sales in week 1 and week 2 of subs campaigns in the past, but I'm stumped on why it doesn't show up that way. It's as if not all the seasons start at zero. (For example, right now, the chart below is giving me figures for week 27 in this year's campaign, but we've only been on sale for 21 weeks.)

Thanks for your help!