yartzeit mistake

hi. I have created a yartzeit calendar containing 11 names, and downloaded it to my google calendar. everything works well, EXCEPT, one of the names populates on the wrong date! I have deleted it from the yartzeit calendar and then entered it again, I have updated the yartzeit calendar, I have deleted the calendar from my google calendar and readded it, and this one yartzeit always comes back as the wrong date! I am really at a loss as to what the next steps are to fix this problem. Thank you.