[drc]

I've never heard of that circa 1910 = 1910-19 standard before, and don't consider 1918 as circa 1910. Circa means plus or minus a few years of the date. 1918 is circa 1920.

However, there can be a little looseness to the +/- number (2 years? 3? 5?) as in practice the dater and buyer don't know the year the item was made. If they knew, there would be no need for the circa.