Back in the early '90s, an envelope was delivered to me containing a physical 3.5 inch diskette. The contents was a Smalltalk/V 286 image file. A bug had been found in a program I'd written a couple of years earlier.
The client had saved the program state (including the full dev environment) at the bug (and exported their current data to CSV files, just in case). I stepped into the debugger, fixed the problem, saved the new image file to a 3.5 inch diskette, went to the post office and sent it back to them.
Of course they had continued working but I don't recall which approach they took to merging their new data with the corrected program.
The client had saved the program state (including the full dev environment) at the bug (and exported their current data to CSV files, just in case). I stepped into the debugger, fixed the problem, saved the new image file to a 3.5 inch diskette, went to the post office and sent it back to them.
Of course they had continued working but I don't recall which approach they took to merging their new data with the corrected program.
The past is a foreign country …