Investors stuffed a net $12.31 billion into stock mutual funds in January, despite the market’s fall. It stopped two months of outflow, including December’s $23.95 billion. It was the strongest inflow since February 2014’s $19 billion, according to the Investment Company Institute. Signs pointed to weaker inflow this month. Mutual funds that invest primarily in the U.S. had January inflow of $6.53 billion vs.