Anecdotal evidence (*1)
We had a bank as customer with branch offices all over the state. These were the 70s, the final years of batch only, although, already using remote batch with local data acquisition and storage. In this case all daily bookings were collected on 8 inch floppies (well, one was enough for a days work). During the late evening the main data center called each branch and requested all batched data entry. It got transferred into local spool and processed. All output, most notably all printouts from jobs and such requested for branch usage or customers, were spooled into transmission pools. Later, during early morning the branch office was called again and all collected data transferred, either for direkt output (print) or again locally spooled onto floppy disk for printout as soon as the clerks started their shift.
So far much like early batch without moving punch cards and print outs in return around the state or later remote batch with punch card reader and printers at each branch office. Except that late stage offered input on keyboard and CRT with nice forms offering support for correct entry and prevalidation against whatever rules there were for account numbers and alike.
At one point a branch office reported transmission errors. Batch data was incorrect and rejected. Service man went to site, but couldn't find anything, all was working properly, including the drives. In the following weeks an increasing error rate was reported. Each and every time the system was checked and found working flawless.
The situation escalated rather quick. At some point not only parts, like floppy drives, but the whole remote setup was replaced by factory new components. By that time customer - for sure not a small one - already threatened cancelling all our contracts and remove our hardware from all of their offices including the data center - mind you, a rather big customers with multiple CPUs alone in the data center for that state.
Amids all of that trouble, one day the field engineer was once again at site. By chance he had to remove a floppy from the machine. Something usually never happened, as by customer process, all data had to be removed before non-bank-staff could do anything with any of their machines.
Guess what, one could see thru the floppy.
Not just badly worn, but the magnetic coating was outright polished away, all the way to the transparent carrier film.
Of course the story was now revealed fast. Each of the clerks had his own floppy, and this guy had used this very same disk since the day he was trained on the new system about a year ago. No need to say that some education happened. In turn the bank ofc had to pay for all the effort - and as well kept a good customer for years to come. The floppy was kept as kind of a trophy and shown to new apprentice and non believers:))
So, I give you several hundred hours of continuous use before a late 1970s 8" floppy quits.
The most amazing factor here was that the drive was still able to read some data, althogh almost no magnetic surface was visible anymore.
*1 - I have a strong feeling I told the story already on RC.SE, but couldn't find it. Maybe it was in comments. Success: Schezuk found it.
