A heck of a mess (Estate/Insurance)

My grandfather died in September. I am the executor's (my father's) designee for the purposes of handling the massive amount of paperwork my grandfather has amassed over the years pertaining to life insurance. I have boxes full of policies, certificates, letters about policies transferring from one carrier to another- and a lot of advertisements for insurance products grandpa may or may not have purchased. As I sift throught the stacks, I am calling insurance companies with regard to specific policy numbers because I don't know how else to go about it. I have found a good bit of active insurance, but I have found a whole lot of inactive policies, too- ones that have either been paid off, have lapsed, or have been surrendered. I've long since sorted the paperwork as best I could, but the other day I called an insurance company in regard to a specific policy only to find out grandpa had two other insurance policies with them which were in force at the time of his death. I have been through every sheet of paper in these boxes trying to find paperwork for these policies. It just isn't there. I've said all that in order to ask this question: Because I am concerned that there are policies in force for which I have no paperwork, how can I go about finding out about these policies? It almost seems like a fool's errand to continue in this manner. (I am trying to get a list of his bank account activity in the months before his death and records from his dozens of credit cards in order to determine to whom he was making his premium payments, but I am concerned about paid off policies and companies with policies on Grandpa who don't have his most recent address.) Any ideas would be much appreciated.