It's good that the Broker gave you a full release if the agent failed to live up to promises or commitments made. Your math is correct, however, in beginning the count from the date of the listing expiration.
The time period a broker will list in their contract will often have to do with the type of marketing commitments being made. There should be a relationship between the investment risk and potential reward. Example: A listing brokerage who agrees to a large scale promotion involving thousands of dollars for a 1.5M home may ask for longer than 6 months, even up to a year. A listing broker who simply throws up a listing in MLS and lets an auto feed send it to some other websites with 4 pictures may consider 60 days quite reasonable. When evaluating the length of time for a protection period, draw upon a look at the whole picture and what the agent and company are investing in the marketing and promotion of your property.
rockinblu....best wishes for a better working relationship w/ your next Realtor.