Uh, actually, if you look, at a certain point, to somehow salvage/keep coherent the age element, Zorlun had to make them say Myriam and Anthony had been together somehow less than a couple of years - that for me does not count as a lot of time, but I guess it depends from the parameters.The censorship is "He's her partner's son from his previous relationship, but they've been together for so long that they have a mother and son relationship even if they aren't blood related and her and his father never got married for whatever reason." It's incestuous in the way that matters to me, which is in the familial relationship. (Making them blood related adds some extra spicy taboo to the mix, but it's not what makes incest hot, imho.) Compared to most other games where it gets censored with a nonsensical "She's his landlady but also drives him to school and makes him breakfast and kisses him on the forehead every morning" relationship, this game doesn't really need a patch to fix it.
Though I completely agree with you that the approach Zorlun found is much better than the "landlady" stuff.
Actually, from your point of view it may seem simpler, in reality the fact Zorlun did not use the "landlady" approach, and could not use it (since he had not foreseen having to change the original family setup with Myriam and Anthony parents of both Katherine and Marc), makes a bit more complicated creating the patch, because I cannot just replace the word "landlady" with "mom".
But even so, I prefer the approach followed by Zorlun, than the "landlady" approach.