My guess is that the "online certificate of title" is not considered the official record maintained by the office, but I do not know what is required in MA.  As an abstractor, I think it is incumbent upon you to report what you find - let the client know where it is and isn't indexed.  Clearly, you found it so it appears to be of record.

The real hazard in these cases, in my opinion, is that if the document does not appear in the OFFICIAL records of the county, it may be subject to attack by a bankruptcy trustee.

I would hate to be the abstractor who misses this because he or she relied on the "online certificate of title."