It sounds to me like there was a glitch in their system, that allowed you to see all the past shows.
When you sign up, your membership starts with the current show and any new ones that are available during your membership period. If you only paid for 6 months, then you only get to see the shows that are released during that 6 month time frame. If you let your membership lapse, and wait 2 months to renew, then you will miss the shows during that 2 month time, and would have to purchase past shows. Your new membership would start with the then current show again.
If you want to watch any past shows, you do need to purchase them.
When this site first started, they only had the shows available for about a year, then they would no longer be available to view, other than purchasing the DVDs. Recently they have changed that, and now they have the ability to let people "purchase" past shows, and watch them any time they want to. So if you weren't a member during a Series, you can choose to purchase just a few or all of them. Those of us that have been members from the start have access to all the shows that have been released. Someone that recently has become a member, shouldn't have access to any of the past shows, unless they purchased the right to view them. I do know that they allow free access to some shows now and then.
Instead of being upset that you may need to spend more money to view the old shows, count yourself lucky that you were able to see them at all. And now, knowing what was in the show, decide if you really want to spend the money for some of the past shows, instead of purchasing past shows, only to find out you didn't like it. You can buy them as you can afford to, and they will always be available to you once you do purcahse them, so you don't have to try and watch them in a short amount of time.
Diane in Colorado Springs