Time flies

Just had a very peculiar experience, almost a Seniors' Moment.

The man from the city gas company came by to replace the meter, which they do at regular intervals. (Meters, like clocks, don't run exactly true. The meter arrives correctly tuned, but drifts out of alignment with passing time. The idea is to exchange the meter before this difference becomes large enough that the customer might have cause for complaint.)

As the job was done and the workman was leaving I said, "see you in two or three years". He looked up, surprised, and said that it should only happen every eight or nine years. I looked down, surprised (did I mention that he was quite short?) and said that I thought it had happened at least twice, at around three year intervals. So he put everything down and got out the charge sheet, and showed me that the meter was last changed in November of 1996.

What happened to those eight and a half years?