There are still significant purchases made late December and...

There are still significant purchases made late December and early January at $17 and we don't know who they are.

Take a look at the volume mid to late December and early January. Historical course of trade information would reveal the extent of the large purchasing amounts. RIV will be reporting half yearly results before 28 Feb and listing their top 20 shareholders which no doubt will be great reading.

CSN didn't start increasing their RIV holding until 1 Feb, soon after the Indian consortium decided not to counter bid. So IMO their holding is strategic rather than financial.