I believe that "certificate holder" is different from a "named insured."  While I would never add a client as the latter, I don't think there is a problem with the former.  It is my understanding that being a "certificate holder" would entitle them to a notice of any changes or if the policy is canceled. 

I think this might be useful because I have heard rumors that some abstractors were buying a policy by financing the premiums, then after they got their policy they would cancel or just stop paying the premiums. This allowed them to provide proof of insurance for a year, even though they canceled the coverage. 

I would check with your E&O agent and ask them exactly what it means to be a "certificate holder."  If you get more information, please share it with us.

Best,
Robert A. Franco
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