I also recently noticed that there is an icon displayed now that says "'Exchange reserve data available" or even"Reserve audit available" behind the name of the exchange if you look them up at coinmarketcap. So far it seems like that only Coinbase and Kraken have finished their audit of the reserves from the big exchanges and the one from Binance, Kucoin and others are still ongoing.
So in theory it is definitely possible that the reserves of Binance and Kucoin are not really existing in the way they proclaim and that they have just moved around assets in order to make the impression like having enough reserves. So we can just wait for those audits and hope that the auditors are making a good job.