
and I may be wrong, Patek Philippe revised the position of Moscow(or should I say corrected it to +3) at Basel 2016. This change also applied to the new world timers 5230 and 5930. The 5131R with Moscow at +4 was produced between Basel 2015 (when the 5131R was introduced) and Basel 2016. Also note that at Basel 2016, Patek had decided to replace certain cities like Riyadh with Dubai, Noumea with Brisbane and Rio with Buenos Aries. I believe there were a few other cities too that names were replaced.
Best wishes,
Sham