A free program like DVD Flick can scan a disc and give it a clean bill of health if no bad sectors are present. It's a pain since it's tedious the more discs there are, but obviously something of that scale could easily take years before viewing every last disc where as even 131 discs could be...
I believe the film is actually called Gaslight, not Gaslite. Both films were excellent (There was a British film first, and half a decade later in the mid 40's, an American film that is widely considered a classic), as was Midnight Lace later on with Doris Day which clearly took some inspiration...