2. 13F Reports Only Require Long Positions to be Disclosed: An investor may gain confidence in their position if they see that an institutional investor is long the stock. However, in theory, the fund can hold an equally large, or even larger, undisclosed short position. In other words, the portfolio manager may have a complex position betting on the stock to go down, but the 13F disclosure shows that the manager is instead bullish on the stock.1. 13F Filings Represent Stale Data: The biggest trap amateur i ...