I can't speak for 'shortsqueeze' and to clarify, the posts I generally post on here are 'daily short volume' not 'short interest' - these are two different numbers/values and are to be interpreted differently.
1. I post a number daily from shortanalytics.com that provides the trade data for that day and I think (don't have it open right now and can stand corrected), the previous 5-6 trading days as well.
2. That number is sourced daily after market close directly from the exchanges.
3. It provides a value for the volume of short shares traded that day (and the previous 5-6 as mentioned).
4. Short Interest is a 'point in time' number. It is reported by the exchanges every two weeks and provided on numerous sites (I tend to use Nasdaq.com). It is however, 'dated' as it reported some time after the actual date its reflecting. (ie November 15th short interest just came out). ie its a lagging number/dated.
5. The reason I post the daily short volume is to give people an idea how how the shorts are behaving from the date of the most recent report to now. It allows us to 'guestimate' a bit on whether the most recent (yet dated) numbers provided for short interest are likely higher or lower than the 'actual' number as of right now. These numbers let us think about how that number may have changed from November 15th (the day of the last short interest numbers) to today. In fact you can even select 'data' on that site and see the short volume back to november 15th and get a decent estimate of short interest to today. The only issue is you don't know how much of the subsequent buying is covering so you can never be right on the nose.
6. As for market data sources, they are always difficult, even Bloomberg is off alot etc...best way to ensure you have the right source, is use the exchange numbers if available and check on other sites as well as a proxy. Also, if a number seems 'off' compared to a reliable source (like an exchange) it likely is.
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