The history of this troubled area is a difficult puzzle to unravel, but I will do my best.  If you are to try to figure out when your (possibly Czech or Bohemian) jewellery was made, you need to understand the timeline which follows.

Prior to the formation of Czechoslovakia following the end of the second world war, the majority of lands in that region fell under the rule of the Austro-Hungarian Empire (1867-1918) owned and run by the mightly Habsburg Dynasty.

Within the Austro-Hungarian Empire at that time were Bohemia, Silesia, Moravia, Slovakia, Carpathia and Ruthenia.

Slovakia, before 1918, was part of the Kingdom of Hungary, along with Carpathia and Ruthenia.
What is termed the ‘First Republic of Czechoslovakia’ was formed at the end of World War I in 1918.  In this form, Czechoslovakia continued until 1938.  So any vintage costume jewellery which is marked ‘czechoslovakia’ or ‘czecho-slovakia’ or even ‘tschechoslovakia’ were all made sometime between 1918 and 1938.
Vintage costume jewellery coming out of that area was rarely signed.  And when they did sign it, it was usually on the most unobtrusive place you could imagine.
I have found signatures under the barrel part of the typically ‘trombone’ clasp.  I have also seen them stamped into the tiny jump ring between the end of a necklace and the spring ring clasp.  They simply did not think that these ‘trinkets’ were worth signing – they would be amazed at the interest shown in their work today.

Nazi Germany took over or annexed Sudetenland  in 1938. (Sudetenland is the German name for the western parts of Czechoslovakia specifically the border areas of Bohemia, Moravia and those parts of Silesia formerly associated with Bohemia).

The Germans held Sudetenland until their defeat in 1945.   The Nazi storm-troopers evicted the peoples of the Sudetenland and marched them further east, with only the personal items they could manage.   Many of these helpless civilians perished in the Nazi death camps, including the talented and hardworking Neiger Brothers from Gablonz.

There was also a Protectorate of Bohemia & Moravia (1939-1945) as well as a Slovak Republic which ran concurrently to the Protectorate of Moravia & Bohemia.

At the end of World War II in 1945, began the Third Republic of Czechoslavakia (CSR).   This lasted only until 1948 when the country was declared a ‘people’s democracy’ (without a name change).
In 1960 the country was changed to ‘The Czechoslovak Socialist Republic (CSSR).  This lasted until 1989.
1990-1992 saw the country being termed ‘Czech & Slovak Federal Republic (CSFR).

After dissolution in 1993 what remained was the Czech Republic and Slovakia.
Looking at a map of the area is certainly helpful when considering all these crown lands and areas which fall under other monarchies.
If you are trying to ID a piece of VCJ (vintage costume jewellery) which you suspect may be from this area, contact me and I will try to help.