Wallet Card at Instructive Books in Baldwin, NY

I've become so interested in old signs that have survived their business that I have been keeping an eye out for them as I drive around Long Island. I noticed this sign for "Instructive Books Inc." on this empty storefront on Grand Avenue in Baldwin this weekend.

They apparently sold encyclopedias and dictionaries. The most recent mention that I can find via google is an ad from 1949. I imagine the company is long-defunct but 66 years is an awful long time for no one to have painted over the sign. Anyone know of a way to research when the company did actually go out of business?