Yes, a single test user will get only 5 auto renewals from a subscription and then autorenewing will stop. I believe they are, or have modified the system so that a test user can be retried - a new purchase by a test user may result in another 5 additional auto renewals.
What I was suggesting was adding to your code running from Xcode something like a big button and a BOOL variable called "fakeCancellation". If the user taps that big button then fakeCancellation is set to YES. When the code searches the receipt for the cancellation_date field iand does not find it, it checks the value of fakeCancellation. If it is YES then it pretends it found that field with yesterday's date.