Per Pivotal, copy and pasted below. Apparently the foreign models output directly usable data regarding p-type.
"ECMWF, UKMET, and Environment Canada models keep track of precipitation type in a precise way as the model integrates, so we know how exactly much precipitation falls in the form of snow (at least, based on the model’s internal diagnostics). This eliminates any concern about including sleet, graupel, or rain when we compute snowfall for those models.
For NCEP models, the bookkeeping for precipitation types is less precise, so mis-categorizing some of the precipitation that fell between data output times is always a risk during mixed precipitation or precipitation that is rapidly changing type. We have adopted an approach that usually avoids erroneously treating sleet as snow for NCEP models, so you should not see a shield of "fake snow" extending well equatorward of the actual snow-sleet line in a large mid-latitude cyclone, for example. Still, it is inevitable that we will sometimes overestimate the fraction of mixed precipitation falling as snow in borderline and transitional environments (usually small in area)."