This has been going on for TOO long! I bought all the Alex Lifeson lessons around 2009 or whenever they first came out. About a year or so later, I needed to re-download the lessons and couldn't, unless I re-purchased them.
I've called Apple support 3 or 4 times about this issue over the years and even they seem to not know why its not working. Of course, order histories only go back 18 months, so your screwed with the "suggested" way of re-downloading these lessons. Even when they showed up in my order history, I couldn't re-download them. The system would not let me.
It's been years now, with still no solution.
I asked the Apple support rep, if it would be possible to refund my purchases or give me a credit I could use to re-purchase the lessons, and even that was apparently impossible to do.
So the solution is: "THERE IS NO SOLUTION".
If you buy the lessons and accidentally erase them and have no backups, your screwed.
No wonder the lessons section has not expanded much over the last 5 years. Because people certainly do not like being screwed over like this.
-Chris