I got an impression, than the "non-cycling" lamps are the USV - as the sodium get consumed, only the mercury remain so it turn into bluish glow at the EOL, instead of the usual cycling...
And for me it is quite surprising the USV were offered only in Europe, with the dosing sensitivity and the impossibility to "refill" the gas from some reservoir I would expect it would not be possible to design for the European tolerance requirements (they would be even stricter with the MV ballasts, as these are designed for higher arc voltages)

You are right, the non-cycling types are often USV.  In fact in 1994 when the first USV lamps were launched, Sylvania marketed them specifically because of the non-cycling feature and tried to persuade local authorites to invest in these premium-priced lamps to avoid the complaints that sometimes come from residents annoyed by the cycling, as well as to make it easier for maintenance crews doing spot re-lamping not to miss lamps which appeared to be working but were in fact cycling.  In USA there was some success and they continue to sell the Lumalux Plus types that way as direct replacements for standard HPS (see http://assets.sylvania.com/assets/documents/HID_PIB1.ba510882-3f83-4639-a430-9e59a92c4ed9.pdf).  However in EU the uptake was poor.  The USV designs survived commercially only in the form of the mercury retrofit lamps.  It seems in that sector that some customers are willing to pay for the longer life and bigger energy savings (= faster payback) that are possible with Xe-filled USV lamps vs the ordinary Ne-filled retrofits.