Hello Cyclejim,
Thank you for using Apple Support Communities. Based on your post, Siri is providing you with the incorrect date for Mother's Day. We'll do our best to assist with this.
To determine if this happened on our devices, we tested this out by asking Siri, "When is Mother's Day?" Siri responded with, "Mother's Day is on Sunday, May 9th, 2021." Which is currently correct. Are you asking something different or for the date in 2022?
There doesn't appear to be any current outages for Siri: System Status
Check the Time & Date on your iPhone in Settings > General > Time & Date to be sure it's set properly for your location. You'll want to do the same thing for Settings > General > Language & Region to confirm your location is correct (for the US).
Also, check that the language is set to 'English (United States)' in Settings > Siri & Search > Language.
If you're asking for a specific year or in another manner, please reply letting us know more for further help.
Wishing you the best, take care!