I think they are, but it also depends on how people are defining things like “accident” and “planning”.
To me, “planning” is an active process. Your parents and family have told you of the many years they tried for kids, in these times, people are using their cycles to match their fertilities. It also means using birth control to avoid the kids, and choosing the exact time of conception (say, getting pregnant during these months so that my kid will be born before the start of the school year, or timing it to some other event).
An “accident”, though, can also have different meanings. It can be those that made it through birth control (when the parties were intentionally NOT trying to conceive).
But what about those, like me and I suspect most of humankind… where it “just happened”? They were not actively trying to get pregnant, but they were not too cautious preventing one. Are those accidents?
In my case, I put myself as a yes, but only a little. My parents, although dating for a long time, where still unmarried (and I was the reason for their marriage). OTOH, I’m sure my older siblings (by dad’s ex-wife) were the same as I was. Not actively planned, but no birth control was done.
I don’t think myself as “planned”, unless you define “planned” as “oh well, they wanted kids some day”. And I don’t think of that word that way.
I have to say, when I read some of the reports about “Oh, I was planned” by people born much more earlier than I… I kinda don’t believe it. You were not planned. You weren’t “unplanned”, but I’m sure you were just a “it happened”.
And btw, you may well have been, for your parents, the best thing that “just happened”.