This post explains all the things that can go wrong when lenders assign mortgages. (Also see this follow-up the same day.)
This post explains how those errors are dealt with (or not) by MERS, the electronic mortgage registration system that supposedly "inoculates" ultimate mortgage holders and securitizers from errors further back up the chain. The writer thinks the Kansas opinion holding against MERS and all the wild claims for it made on the internerd are a "nothingburger" but still concludes:
I think the important question is whether, on balance and in the aggregate, the MERS system works well enough to allow lenders to re-start the private label securitization money machine in a few years. I think the answer is probably no.