It's also possible that in some places there were a few issues, but people looked at bills for 100 years of electrical service and said "Yeah right," and fixed the now-easier-to-find code that still used 2-digit dates. If that only happened a few times, the extra work involved in working out the January bill by hand (or waiting until February then billing for 2 months) wouldn't cause too many issues in the economy, and anyone looking in from outside wouldn't even realize there had been an issue. If it happened everywhere the economic impact would be more noticeable from outside.