Certifications (Rating) for a Television Series

Should the certification (ratings) for a television series be attached to the main series page, or be attached to every single episode page of the series?

I've come across instances where there is a rating of US/PG on the series main page, and then each episode is also given a rating of US/PG. However, at times I've seen the notice "While data in this category can be added at the episode level, you should try to enter it for the entire series if at all possible," when making corrections to episode-level certifications, and other times there is no such notice. I get that when a particular episode's rating differs from the series overall, that should be noted. But is there a standard for the redundant series-level/episode-level certifications?

I've also come across cases when removing bad/redundant certifications on episodes [for example Canada/C8 (Québec) and Canada/C8 (Quebec) not both being needed] that sometimes the change goes through with no problems and other times it is rejected as "Does not meet contribution guidelines."