one guess: they are very focused right now on saturated & trans fats, so those are likely to be accurate (unless the numbers are totally missing) and they may be undercounting other subgroups (poly & mono).
another trouble may involve how to count certain fatty acids that are technically saturated but behave in the body more like mono (for example, stearic acid, the primary fatty acid in lard, that is, pig fat).
also, there's a lot of pressure by the meat folks not to reveal how much trans fat appears naturally in animal products, b/c all the evidence against trans fats so far blames only artificially created trans fats, but no one knows for sure & meat/dairy producers don't want to be painted with that same broad brush. but i can't imagine there's that much trans fat in tri-tip to account for your discovered discrepancy.
also, what i'm finding is that the USDA & their counterparts elsewhere are reluctant to "impute" (guess at) missing data, and the quality control in the underlying studies is often atrocious or nonexistent, even for basic & obvious commodities like whole and skim milk.