API Ammonia Test Kit

I have just had a bit of a shock and got confused while reading up on Ammonia tests.
I use the API test which is labled as a NH3/NH4+ test and this is Total Ammonia Nitrogen (TAN), not a NH3 (Ammonia) test. The difference between the two is rather important because the NH3 (Ammonia) is the dangerous part of TAN while the NH4 (Ammonium) is considered non toxic.
The limit for NH3 is generally taken as 0.02ppm and the amount in a TAN reading determined by the water pH and temperature. For my tank parameters I would theoretically be able to have a TAN reading of 7.5ppm (seems a Hell of a lot, but that is the maths) before the NH3 level hits 0.02ppm.
I obviously don't run at this level, the test read in a colourimeter normally indicates 0.07ppm so by calculation NH3 is 0.00013ppm (that seems a better number)

Well today I saw the the API test use a Salicylate reagent, I googled this and saw that it tests for NH3 so the result would be 375 times more toxic than the bottle label suggests. Eek!

So here is the confusion, if the API colour chart doesn't start to read until 0.25ppm, this is 12.5 times higher than the maximum safe NH3 level I assume that Google or the API instructions are wrong and this IS a TAN test.
Anybody seen an explanation of this ( @Sue I'm looking in your direction  )

Thanks @barneyadi The Excel I sent you actually already does this calculation - assuming the API Ammonia test gives a TAN value.

Thanks @Sue, this had to be the answer or all our fish would be long dead but it's good to know the reason. So Google was both right and wrong when it said the salicylate tests for ammonia, it does but only after converting the NH4 so the test reads both NH3+NH4