I respect Dan and Swampy so much, but I also don't subscribe to the idea that every word out of their mouths about canon lore is gospel.
Really, so much time has lapsed between the actual production process of any episode from the original Phineas and Ferb and now (and so many original screenwriters for the show haven't come back for the revival) that one should reasonably expect for some of the original intent and context behind minor decisions to be lost.
Also, sometimes not a lot of thought is put into a decision at all. These are happy accidents in production! Continuity, chronological timelines that make sense and whether or not Ferb's full name is "Ferbs" is NOT the point of the Phineas and Ferb show. The insignificance is oftentimes actually the point of a decision in a comedy show - because it's funny, or at least makes someone on the production team smile.
And to retroactively assign meaning to a thoughtless choice is... well, it's pretty shark-jumpy. There's no point to doing it other than to invent new content for fans to enjoy.
So unless something Dwampy say makes sense within the context of the Phineas and Ferb universe - or indeed unless it's painstakingly clear that their statements are backed up with original intent - I'm quite happy to take "official" lore with a grain of salt.
Let the headcanons run free and wild like mighty stallions!!!
Here are some of mine that directly contradict the word of Dan and Swampy:
Linda and Lawrence were actually sweethearts prior to either of them having kids - this is when they actually attended the Love Handel concert together. Then something happened to put a pause on their relationship (Linda becoming Lindana, or Lawrence needing to go back home to England after his wonderful summer romance, or both). They reconnect after Linda has Phineas.
Phineas and Candace are half-siblings; one father was a donor from a sperm bank and the other was a brief boyfriend during her stint as an Astrophysicist. (Not Doofenschmirtz)
Ferb's full name is actually "Fergus" or "Ferguson". Phineas mistook the name as a tiny wee toddler and couldn't comprehend that "Ferb" wasn't his actual name - because Ferb was answering to him perfectly. And so the cute, silly nickname spread, until it was irreversible.











