This map shows the year in which each sheet was produced. The dates range from 1820 to 1826.
The west-to-east progression is clear. But is it meaningful? Does it reflect (an imperial) hierarchy of significance? Does it hold that the later the sheet was produced, the lesser the significance of the territory it described? Perhaps that is reading too much into a meager bit of evidence.
Perhaps, instead, the chronology of map preparation suggests an evolution in cartographic expertise? Why not start with the low-hanging fruit and then move on to tackle the more challenging maps? The relatively late mapping of the Grand Duchy of Finland and the Caucasus, which present unique challenges due, respectively, to their coastal and and mountainous geography, might support this observation. (A bit of digging in the archives would, of course, yield the answers.)