Have seen a few EPROMs on boards for equipment like Fire Alarm / F.L.S., Security equipment, Lighting / BAS / EMS controllers, which were missing the label that covers the erase window.
To avoid the same situation of accidental erasure, I place a thin strip of duct tape over the window, and build up a few layers. Hoping this may at least reduce the problem.
Maybe the glue didn't hold well on these EPROMs, or maybe it as Bjarney said - Firmware upgrade - but the PROM never gets recovered after the flash.
It's easy to see the ones with firmware upgrades which were recovered. The label has revision notes on it, or a small label covers the original sticker.
Nevertheless, that story of Bjarney's is a real eye opener!!! Sure makes me think twice when taking pictures of equipment!
Q?: How do you ruin someones whole day/week?
A: Uncover an EPROM and ask them to snap a picture of the board!
Should be submitted to the "Poop Occurs" section of trade magazines.