Installing axle-backs -- clamp doesn't tighten?

I recently picked up a pair of nearly-new Magnaflow axle-backs for my 2010 GT.

The pipe tightened down just fine on one side, but on the other side the outer pipe would not tighten down on the inner pipe.

I noticed that the band clamp sits about 2/3 on solid pipe with no slots; when I see this, I cannot figure out how this can possibly work -- how can a band clamp compress a solid pipe, with no slots or anything to allow it to compress?

I extended the slots a bit with a sawsall, but didn't want to go too far . . . this helped a bit, but the pipe still was not tight, I finally got irritated with it and put a big pipe on the wrench and said to myself "this f-ing thing is going to either tighten or break" and sure enough the clamp broke.

Has anyone else run into this problem? What is the solution? I think I need to extend the slots in the outer pipe to allow it to compress, but I want to make sure that is the right solution before I ruin the mufflers. Obviously I would not extend the slot beyond where the clamp covers it, but probably need to go pretty close to the edge of the clamp.