The unfortunate part is that it CAN show up as "pass" on the FAA report (for the most part and at least 99% of time). Majority of the report is what the unit sent.. there's some position verification (using the radar) but the unit it free to send out any signal it wants. (ie fully compliant even when it's really not).
Another competitor sends out "unbelievable" numbers -- such as GPS "accuracy" that is 2 orders of magnitude more precise than Garmin 430W and SIL and SDA numbers that don't pass the smell test.. So the FAA report just shows that -- what the unit sent.. Doesn't actually mean those units meet the performance standards..
It's an "honor" system for the most part.. and some units may either abuse it or stretch the borders a bit with that.