To think this is batshit in the extreme?

[AintNobodyHereButUsChickens]

My son is 9 now, me and sister in law were pregnant at the same time although I was due a couple of months before her. She never said it to my face but she was furious that I'd gotten pregnant before she had, it meant that I would give the in laws their first grandchild and she wouldn't. Anyway, as I was nearing my due date she used to say stuff like "If my DD was born now she'd be the eldest instead." (Bearing in mind that she was due two months after me!) On a few occasions she actually said she wished her DD would be born early and she would hint that her consultant said he needed to do an early Csection The babies ended up being born in their intended months, mine being first.

Anyway fast forward a few years and they moved away to the opposite end of the country and we hardly see them anymore. Recently, DN came up for a visit and her and my DS got talking about their birthdays and their ages and who was the oldest etc. They got into an argument because DN was insistent that her birthday was.... three months earlier than it actually is. DN came and asked us when her birthday is (she was at our house at the time) and we told her when it was, her real birthday, we showed her on the calendar. And she refused to believe us, she kept saying "So my mum's been lying to me my whole life about when my birthday is? My birthday is not 'X' but actually 'Y'??" We got her to ask MIL when her birthday was and MIL was like "Errm, it's , why?" And DN just kept saying "So my mum's lied to me this whole time?"

What the hell?! Who does that??

I’ve never heard of a register being in age order, always alphabetical.
Class teachers ask the kids when their birthdays are and as far as I know. No. You get a list from the office or it might be in the register.

DH had to get his year 5 class to write down their birthday the other day. About half didn’t know the day or month.

I wonder if schools do it differently then?! My registers, from two different schools, were definitely by age but they were both mixed age classes. So the register also separated them by their year groups.

This is right up there on the list of craziest things I've heard!!
Mind I know someone who when they told their family they were pregnant their sister's first comment was when are you due as so am I whose going to give our parents their first grandchild. Not congratulations or anything 🤦🏻‍♀️

This makes me very worried, why would they think this lie is necessary? what else have they lied about?

Very batshit YANBU

Batshit, crazy. How long did she think the lie could go on for and why had her dh not corrected her? Though to a lot of people having provided the first grandchild is very important. I got engaged five months after my bil got married. Sil openly admits she started trying for a baby straight away as she wanted to give inlaws the first grandchild. As it was I waited a year after we got married to try to conceive and then had two kids after quick succession. Imagine the horror on my sil's face. She too is batshit.