No producer mark but generic country-of-origin designation with Czech ‘C-hatschek’ initial, therefore (as mentioned yourself) approx. 1918-1920/21.

Hold in mind that many lamp producers held back store for decades (no demand, out of style, for certain projects only); also some lamps I have seen were later refurbished and rewired. Mixed dating periods are not unusual.

This is an image of the mark.

Will check back later this week !!

Later this week

Can you post a pic of the lamp and one of the mark on bottom ??