What's so complicated about it? probably I didn't get it?
In the main league pages, Recent games, stats, playoffs, There's a select box on the top WHICH is telling you what season you are viewing.
You can set set it to all, it means it will calculate all the seasons together.
for example, If you set it to all in the stats page, it will give you the stats of the people by "season 1 + season 2".
It is a good thing to compare seasons together.
for example you can check stats page to see which people was the top 10 in season #1, then make the time goto season 2, and by a click you can have the top 10 in season #2 or top 10 summing all the seasons together.