Bitfinex barely holds tether. The rich list you see shows how much each exchange has on behalf of their users + their own. It has been as low as 1.8m some days. https://i.imgur.com/3mm5ot1.jpg
Considering there is much more you can use tethers for on bitfinex than bittrex and that bitfinex volume (even excluding shorts/longs) tends to be equal or higher, the amount of tethers people "have" on bitfinex should be much higher than what people "have" on bittrex.
The only reasonable explanation for this discrepancy is that bitfinex is taking the tethers of its users and selling it on other exchanges while having only as much tether in their own possession as they need in order to effect withdrawals by users.
The implication of this is that tethers on bitfinex are "fake tethers". For example, imagine if users found out bitfinex only had 5% of the total bitcoin supposedly on the exchange in their possession.
Further, this means that the total circulating supply of tether is what we thought it was, plus the entire amount that people "have" on bitfinex, in addition to what the people behind bitfinex has credited themselves with.
For all we know there could be up to a billion or even more "tethers" on bitfinex right now.
If the very credible suspicions about tether not being backed by any USD in reality is also true, this could be a case of an entity effectively not just stealing the total marketcap of tethers worth of crypto from the crypto community, but that in addition, circulating "tethers" on their own exchange, and potentially even more given the possibility of using those "tethers" to manipulate both prices and meet the other side of shorts and longs.
In sum, a scam with the potential to have siphoned billions of USD in cryptocurrencies, with the bitfinex/tether link only being the tip of a much nastier and much larger iceberg.