Often-times, those shorting to cover with conversions are done and covered in a few days. Those shorts are never counted because they are covered in a short period of time. OTC markets short count is accurate and usually agrees with Shortsqueeze.com, see link.
Did you know that every sell is considered a short sale until the trade clears. When you sell a stock, the info is not immediately available as to a normal sell or a short sale. That is only determined after the trade clears about 3 days later. That's why short sale data is always posted several days after the end of the month and the 15th.