What was the nationality of people who were born and living in Austria-Hungary classed after it spilt?
Also what confuses me is that on Wikipedia it states that Lída Baarová was born in Prague when it was in Austria-Hungary... but her nationality was Austrian 91914–1918, 1958–2000) and Czech (1918–2000) like how did she gain Czech nationality and how come she gained Austrian Nationality , why didn't she gain Hungarian Nationality.
Austria-Hungary started doing nationality census in Bohemia in 1880 and repeated the task every 10 years, ie. the last census was done in 1910. The key identifier was a person's colloquial language (Umgangssprache). This way of processing data wasn't very accurate since it may have put numerous Czechs into a "German" category as long as they preferred using German language on a daily basis, especially if they were city-based and not from the countryside. Nevertheless, the A-H administration was fine with inflated German numbers for obvious reasons.
Independent Czechoslovakia has done its first nationality census in 1921. This time the old A-H identifier was found unsuitable and it was replaced by a person's native language; with the exception of Jewish inhabitants who were allowed to claim Jewish nationality even if their native language wasn't Hebrew.
The English Wiki is therefore inaccurate. If you have a look at either Czech Wiki or German Wiki, both of them correctly say that Lída Baarová was Czech.