Makar sankranti ??

How can makar sankranti is on 18th agar koi aur festival hota tho I can understand but sankranti kite festival one of the only festival that comes on same date every year is on 14th of jan

But in this show celebrate after maira 's bday which is on 17th they said this in episodes so day after her bday it's 18 na so now they celebrate sankranti how cannot understand this logic confused and a big laugh /mistake for makers