It would be impossible for anyone to answer this question without knowing more about your case and reading the letter in question - the entire letter.
Take it to a local attorney for a consultation.
The very first sentence of your entry above says "within two years of the date of the incident". So the letter is not misleading. In addition what we call "ignorance of the law is no excuse" meaning you had a duty to consult with an attorney to find out the time deadlines. Unfortunately, I don't think you will get very far on the "misleading" theory.
I am licensed in California only and my answers on Avvo assume California law. The above answer is for general information only and is based on the information you posted. Every case is fact dependent, so to get a thorough analysis of your situation, you will need to consult face to face with an attorney licensed to practice in the jurisdiction where the incident took place. Do not conclusively rely on any information posted online when deciding what to do about your case. No attorney-client relationship shall be created through the use reading of this response on Avvo. You should never delay seeking legal advice, disregard legal advice, or commence or discontinue any legal action because of information in this response.