3inch grassy stolons pretty much has to be U. praelonga. Cornuta has much shorter stolons that are still pretty "grassy". Of the others, if they are correctly IDed should have flat stolons, at least .5mm across with rounded tips.
If any have pointed tips and are consistently leass than .5mm across and less 1cm long, you have most likely have U. subulata.
I think that utrics are a low demand, low profit plant for most CP nurseries.