The issue in not finding your 1987 certification is almost certainly NOT because they purged old electronic records, but rather because an old paper based record was not added to an electronic database with the advent of the digital age. Some agencies made a greater effort than others to load old records into a modern system.Plastic cards do have a finite lifespan. I used to keep some in my wallet so I could always get fills and go diving. After a decade, several of them started to crack. I took them out of my wallet and put them in plastic protectors. I wanted to see about getting replacements for some of them, but most want $50 a pop. I lost my Nitrox card several years ago, but instead of getting a replacement, I just show the next higher card. Some of them are getting so old, I wonder if I wait too long they won't be able to find me in their database anymore. I contacted NAUI about getting a replacement for my OW card from 1987 and they have no record of me. That's probably too long to expect anyone to keep records. I did see PADI shows all my cards on their website, maybe one day I'll breakdown and order new ones.
And then there is always the possibility of losing an old paper record to fire, flood, vermin, human error, etc.