En masse deletion of incorrect certification from a series?
Brookside. A pre-watershed soap opera where someone has erroneously entered an "18" certificate to every. single. episode. Now, I've so far deleted it from episode one and the overall title, but as there are nearly 1300 episodes, that's a big job.
Now, there WERE some episodes that had an 18 certificate, particularly towards the end of its 21-year run when it got moved post-watershed for some editions. And I think that's where the confusion has come from, as there are some releases with that certificate, albeit sometimes special spin-off shows rather than the actual show itself: https://amzn.to/3Fz8QiY
But as can be seen here, even one of the more violent early episodes involving a gun siege was so tame it got put out on VHS with a PG: https://amzn.to/3ZTZx5c
A compilation went out as a 15: https://amzn.to/3Js1XB5
I don't work for the BBFC, but even just with basic sound judgement I'd estimate that the vast majority of the episodes for at least the first 10-15 years would have been PG, with the occasional 15.