I suspect whenever that happens, Ofcom get some complaints about it. Swearing before the watershed isn't allowed. For the opposite extreme, look at Japan, which has no watershed, and allows blood, death, swearing, all at breakfast time. Bet the Japanese Simpsons dub never gets any scenes cut at all. Shame that can't be said for the original English version.
I am sorry to say but you are wrong, swearing in theory is allowed before the watershed providing it is justified in context it is only the strongest two words of swearing that are not used before the watershed.
Many shows on TV contain swearing before 9pm and a large majority are on Ch4, Bremner Bird & Fortune for example has numerous examples of what many people would class as strong language going out at 7pm
It does baffle me as to why any edits would need to be in, as I doubt any complaints would be upheld by OFCOM anyway