I can find records of fires at other federal offices, but I can't find any record of a fire at the FCC offices. I'm pretty sure that the fire thing is a myth.
Fire may be a myth, but it's a fact that certain archived FCC records were destroyed by water in the 1970s. My speculation is that it was Hurricane Agnes in 1972, and the records that were destroyed would have been archives (not current records) that were in the basement at the time. (At one time, FCC said that records of licensed issued prior to the mid-60s are no longer available. That date is consistent with Agnes.) If you look at the rainfall totals for that storm you'll find it peaked around 15" in an area that looks very close to Gettysburg.
I did not say that records were not destroyed. I only said that the fire idea is a myth and can't be substantiated. And, while the hurricane idea somewhat matches up, it is also speculation. You can probably come up with a dozen different scenarios, that closely fit the dates and times.
Usually, when there is a disaster that destroyed records, or causes wire services to be interrupted, the FCC requests more money. You can find several "Orders" on-line that were generated to help with recovery. And many of them are due to hurricanes.
I am sure records were destroyed, either by accident or on purpose. Which way, really doesn't matter.
And the fact that FCC was able (prior to 1976) to issue unique callsigns indicates that there MUST have been license records at that time.
I never said that the FCC didn't have records. Of course there were records. But when they created the ULS, how far back did they need to go?
I am sure that some of those old records still exist, in one form or another. You can access some of the old callbooks at
Amateur Radio Call Books. But the archive is incomplete. Most of the Call books available only have listings for calls with a "zero". But they may be updated in the future.