I completely agree that the EN250 mark seems to be older than the EN250:2014 mark one would want to see for something tested now. The SS1 has been around for a while, so I would be surprised if they went through a retest phase.
The documentation I found on EN 250 states a requirement for testing in 2-4C water to pass. I do not know if this was concurrent with testing at pressure. What I could find did state that a reg marked EN250 was appropriate for use in <10C however.
This, of course, is based on the limited info I have been able to find on the EN250 standards prior to the 2014 update. I very easily could be mistaken.
For a second stage, one would hope to see something marked EN250:2014 ideally. EN250A:2014 would be something you'd want to see on a first stage as the "A" designates the ability to support multiple second stages in the cold.