Re: KN4 calls - blast from the past !
You are correct. All of the oldest FCC records really were lost when the FCC office in Gettysburg flooded. I believe all the archival records (the non-active licenses) were probably stored in the basement, and were destroyed.
I haven't heard this officially, but my suspicion is that this was Hurricane Agnes in 1972. Check out the rainfall totals from Wikipedia (https://en.wikipedia.org/wiki/Hurricane_Agnes#/media/File:Agnes_1972_rainfall.gif) and figure out where Gettysburg is on the map. I'll give you a hint--look for the dark blue area with the arrow showing 15+ inches of rain.
This destroyed all of the non-current records. And Agnes's date is consistent with FCC statements that "all records of licenses issued prior to 1968" are no longer available. So the only records that exist are any licenses that people still have, and the callbooks.