From: Hex X37, Y15
It's not only broad or narrow. It is three types, broad Russian, normal standard European gauge or narrow gauge. Many branch lines in the Baltics (as well as in many other coutries) were narrow gauge and had low capacity and were not easy to integrate into the German military railroad system, for the same reasons as the broad gauge, separate engines and rolling stock etc. About a third of the railroads in the Baltics were narrow gauge, so out of 7000 km only about 2000 were standard European gauge. Of the rest about half was broad and half narrow.
Comparatively easy progress of German railroad conversion in the Baltics is often alluded to and used in games, but I suspect it is one of those often repeated truths that don't appear to hold up when you look at it more closely. Compare the dates of rail conversion. For example, at the end of August, the railhead in the Baltics was at Luga, but at the same time it reached Smolensk in AGC, and that is almost exactly the same distance!