I had big parties for my DH’s 40th and also my own. Everyone who was invited came, as far as I can remember although DH met up with his friends in the pub the night before. (His was at home, mid afternoon.)
I say friends, but once we had our DC, the friendships fizzled out as none of them had children.
All they ever really did was go to the pub tbh.
For his 50th, I invited mostly family out for dinner. There was about 20 of us and I made a huge fuss of him as he only really has me.
We did the same for my 50th. Both very enjoyable nights.
I make a point of trying to go to every party/event that I’m invited to, even if it means a fairly long drive.
I like to support my family and friends. Sometimes I’ve been the only family member to go!
I’ve gone to parties when I’ve just returned from holiday a couple of hours before!
I’ve gone to children’s birthday parties early on a Sunday morning and dragged two toddlers with me, no sat nav and difficult to find.
A few years ago, I was invited to a former neighbour’s husband’s 60th.
I did know him but thought it was a bit strange. I went because I was invited.
Turned out, I’d got my wires crossed. It was HER 60th! We laughed so much about it and enjoyed the night.
I would absolutely HATE a surprise party.
I’m sure your colleagues thought nothing of it tbh. And as someone else pointed out, no one knows how many were invited, do they?