It is 100% legal to send mailers or put up billboards (which are not as regulated as shared spectrum for TV/radio) with the wrong election date to people, and this happens a couple of times every election cycle. Sometimes its government agencies, sometimes its a campaign (first example that popped up when googling: https://www.newsday.com/long-island/politics/spin-cycle/zeld...). I don't think any of them has been investigated by the FEC.