1990s concrete floors insulated?

Hi guys, this is my first post, im baffled by whether it was common practice to insulate concrete floors by the early 90's or was that a later development? Im looking at a renovation right now and would like to have some idea whether it was common practice or not, any help would be much appreciated as the current owner doesn't know whether the floors are insulated or not and we cannot contact the builder that put down the floor when the place was last renovated its a 1960s house that originally had floating wooden floors, really any help would be much appreciated here