I didn't mean last as in they didn't have any left. My assumptions are that Socius sold after the prior Q earnings call their 3.3 million shares or whatever to get under 10% and make room for a tranche which I believe is what increased the float last quarter. My guess is Socius is selling some shares they acquired from that tranche (if in fact it occurred).
So, There are not too many other institutions that have a substantial amount of shares that ZBB insiders could say, we know you're looking to sell or have to sell, we'll buy these direct from you at X price, perhaps each day.
If it were Ardsley or Marathon they would have to file an SEC filing, Socius would not.
It's all speculation on my part, but it makes complete sense.