Yes, this is well known as a pattern. I definitely had a "fall apart moment" when having children, although given I was 20 and in a shit relationship and had gone from being teachers' pet/top set in everything, to failing or dropping out every post-GCSE course, I don't know how much anyone can say I didn't have ADHD previously. I suppose maybe you could put my fall apart moment at puberty instead.
There were also milder signs before though, like I was just a fucking weirdo at school who nobody liked apart from the teachers and the other weird kids (who, TBF, I adored) because I had close to 0 ability to pick up on social cues in conversations or understand what was fashionable or hilariously unfashionable (I can remember remarks that made teachers cringe). And in every single photo of me as a child I look like I have been assembled from some kind of jumble sale by someone who is overexcited by the concept of glue. And all my reports said things like "Would do great if she paid more attention" "Should stop looking out of the window and she might finish work" "Has such potential if only she would apply herself" "Needs to work on time management and presentation" "Enthusiastic and chatty but slow to complete written work, although it is of excellent quality when it is done". My entire puberty seemed to involve crying constantly/at least 3 times a week, to the point that I was really concerned when DS1 went through puberty and didn't turn into a blubbering mess until DH said maybe that's just a girl thing, and it's only later that I've though hang on - I don't even think other girls were having that much emotional dysregulation (maybe I'm wrong, though.) I had and still have one crippling phobias which are completely stupid but affect my day to day life. I used to lose and forget items constantly, causing much distress (which made no difference to the frequency that it happened). My dad was always telling me "You'd forget your head if it wasn't screwed on!" My bedroom floor was about 50cm deep with unfinished paper projects. etc etc.
And I wasn't actually diagnosed until 7 years after having DS1, because I didn't know that ADHD was related to all the difficulties I had been having, I thought it was just hyperactive kids. And then I was astonished when the doctor said she felt I was a pretty textbook case because I just thought I was a bit shit at life, and yet I was also somehow still thinking that I was presenting an outer image which looked like the way my teachers had talked about me at school.
The thing is that you can be an utter mess, but unless you're either involved in criminal activity, accessing addiction/mental health services or there's a child welfare concern, nobody will necessarily notice. And TBH even if you have any or all of the above nobody will necessarily put it down to anything except for poor life choices, and if it's not bad enough to be involved in any of these, people often notice that you seem a bit disorganised, or lazy, or forgetful but they usually only interact with you in one context, so assume everything else in your life basically functions and don't think any more of it. There's not really any scope to say hang on a minute, this person seems to be really struggling with the basics of adulthood, has anyone screened them for that disorder which can explain these difficulties? I know there have been schemes BTW but they are relatively recent and tend to be hyper-local whereas IMO you ought to be screening everyone who shows up in any of these places all of the time. And while you're at it it would make sense to screen generally too - at least anyone high risk e.g. direct relatives of anyone diagnosed with ADHD, children who have been in care or were born premature, school children who experience a slide in grades or where the teacher suspects intelligence and output aren't matching up. Or just generally in a similar way to how we screen for lots of things. Realistically they can't do this because if you screened everyone the amount of people you'd need to put through a full assessment would overwhelm the system, and it's already overwhelmed. But I think it is happening anyway because awareness is being raised of the more inattentive type presentations and so people are self-screening via the internet, which is sometimes accurate and sometimes is not.
The reason IMO that a lot of adult-diagnosed ADHD pops up as a question in the 4 Ps (Puberty, Pregnancy, Postpartum, Perimenopause - I'd add a fifth - Pandemic) is because those are times that life is generally that bit more difficult for everyone, and so if you have been hanging by a thread then you can completely fall apart. Or it can highlight that while other people around you in a similar stage of life are struggling, you can start to think but hang on a sec - the things they're talking about have ALWAYS been difficult for me, are they not supposed to be?? Or you join in with the camaraderie about it being a hard phase, and then the others pass through that stage of life and it gets better, and you stay stuck in the same cycles.
I think that's why they are trigger points, because there just aren't really any other routine times where general coping skills are looked at, or where differences are highlighted. Whatever your own normal is you just get used to it and assume everyone else is dealing with the same, it's only when you have a direct comparison moment that you will notice.