I hadn't thought of old digital remnants. I still think scraps of paper in the pocket. I'm old school.
But I don't think they had PDAs is 1993 and not many people keep the same cell phone for that long. A 1993 cell phone would be the size of kid's shoebox!
I suppose its all possible, but it still strikes me as unlikely. Maybe some old computer files survived a few computer upgrades and were lurking forgotten in some corner of his laptop.
It could have been in a text file of numbers or in a bunch of old emails. I'm not blaming you for being skeptical, but it is possible.