Glad to see your pictures and information on these less known and climbed peaks... forgot to tell you something, I once asked you about the GPS accuracy well I have worked with two garmins this summer, one like yours and one the yellow one, I compare the elevations with your maps, I found the GPS altitude so accurate that seems always less than 10m differential, but the altimeter numbers the GPS shows have sometimes more than 20m differential.
My measurements too are usually within 10-20 m of what appears on the 1:50 000 maps, although I should say that the GPS seems to take 5 or more minutes before it shows an accurate reading. When I reach the summit, it shows a number that is a little low, but then it gradually goes up until it stabalizes. This becomes a problem if you try to measure the elevetion of a spot while driving. Unless you stop there for a few minutes, the reading won't be accurate.
I don't know why the 1:50 000 map for Siyalan area turned out to have a few mistakes. It showed Siyalan to be 4123 m but my GPS showed 4190-4195 m. The map also failed to show the Kandigan Peak.
Thats because you are reading the altimeter numbers, which is relative to air conditions, the yellow garmin GPS always shows GPS elevetion which is realtime and as I learned somehow higher and more acurate than the altimetere elevetion, the GPS elevation gets more accurate at higher elevations. at caspian sea level 14m false, but at higher elevations than 3200m less than 5m false...
the yellow GPS is good for car uses you can track the elevation meter by metere but it only uses GPS methods and has to be always covered by 4 sats and doesn't track your climb graph, speed... .
With the garmin summit GPS like mine and yours the track and number shown are altimeter numbers which are near(less) than the GPS realtime numbers, but there is a trick to get the quick and more accurate GPS elevation, the calibrate menu-> after two questions shows the GPS elevation to calibrate the altimeter with. I always grab that number as a reference for a point not the altimetere shown in the elevation page.