Does your registry still provide written index books?  Massachusetts stopped printing indices sometime around 2003 for Essex South & even earlier for other registries.  In at least three registries I know of, there are no books of any kind any more.  All the books, including indices, were scanned & the books shipped out to storage.  Not so great, if they missed a page in the index scanning. 

As to missing docs because of Registry indexing errors, I take an exception for that on my Report form.  Running all permutations of the name Smith could take days