Production Codes are the official numbering system used originally by Granada Television and now ITV Productions to document the episode numbers of the programme. Each production commissioned by Granada was allocated an overall code and then an episode number appears with the code. Coronation Street 's production code in 1960 was P228, therefore Episode 1 had a production code of P228/1.
In 1970, the programme reached its 999th episode and, for some reason, instead of the next episode being P228/1000 the programme was allocated a new production code of P694. To add to the issues of numbering that have faced the programme since then the first episode to use the new code was P694/1 and not P694/0 or P694/1000. Episode P228/999 was actually the episode which was publicised as the show's 1000th episode - one episode too early and, to add to the confusion, the countdown clock at the start of the master tape of the episode shows it as both the 999th episode and the 1000th episode. For the next twenty-six years the episode number used within the code was 1000 episodes out.
When the programme reached Episode 4000 on 15th April 1996, the code skipped from the previous episode's P694/2999 to P694/4000 and has been commensurate with the episode number to this day. However the codes are not accurate to the number of actual episodes shown. A handful of codes have been skipped over, occasionally duplicated, a couple of episodes have had entirely different codes used to the normal run and several episodes have been commissioned as two single half-hour episodes and then been transmitted as one hour-long episode with two production codes on its paperwork. Nevertheless, when ITV wish to publicise a "round figure" episode (5000th episode, 6000th episode, etc), they base their numbering strictly on the production code, irrespective of the inaccuracy of using such a system.