I can see that it is nice of you to remember their anniversary but surely the key is that it is their anniversary. I am guessing that at the time they got married you werent around. So, while it is nice of you to send a card it is up to them to decide whether or not to make a fuss.
Mind, I write as one who was regularly guilted by DM (for whom Hallmark was invented) to remember every single sodding event with an appropriate card.
We have decided not to involve our DCs in our wedding anniversary celebrations unless we choose to.
IMO other than 25th the -5 ending anniversaries are just the same as normal ones, although I suppose anything after 30 is a milestone worth celebrating these days. I wouldn't feel too bad about it. For my parents I have done special stuff for 25, 30 and 40 but not for other years.
45 is sapphire! Just rang & seems my brother has completely forgotten!! At least I remembered! My mum said she didn't expect me to buy them sapphires!! I have ordered a lucky silver sixpence from Amazon, it will only be a few days late!! Better make sure their 50th is in my diary though!!