That's what I meant by interleaving. You'd have something like this: (forgive the crude image, but I'm on a PC at work and the tools are limited.)
I'm trying to illustrate that the old data and new data are both visible on the same track. Ergo: read/write errors.
PS - you can get DSDDs on eBay for way less than a buck a piece. <2cents>They're cheap enough that it's worth it to just buy a 10-pk and not muck around with the 1.44s and risk data loss.2cents>