Gwx question: neutrals & lights at night

If I recall correctly, neutral ships running by themselves run with their lights on. My question is this: twice now I've run across Frankreich shipping during the timeframe they are neutral. Both times it was two merchantmen being escorted by an armed trawler, all three under the Frankreich flag. Neither time were they running with their lights on (and yes, both times in question it was night :p )

Should they or shouldn't they be lit?