Missing source code? That's terrifying.

I did some contracting for a retail bank a good while back and the COBOL source for the term deposit interest calculation routine had been lost a few decades earlier but was still in use. I suggested a rewrite but there was no enthusiasm/support for it - especially as my prototype could not exactly reproduce the rounding. Nobody wanted to have to deal with customer communications to explain why one cent of interest was being paid a month earlier or later than before.

Totally normal, happened all the time :))