Interesting, just checked my FCOM (newly released company version valid on january 1st) and the only note referring to cold weather approach and landing is to use normal flaps and speed additives except for non normal situations requiring flaps 15 (not approved as normal landing flap setting) in which case Vref ICE has to be used (Vref 15 +10kts). No other speed additive is mentioned at all.
Could there be an FCOM difference for those planes which have flaps 15 as normal landing flap setting and those that don't?