When you are researching a time period or dressing a set, remember that people do not buy all new things every single year. A real house or apartment is filled with the clutter of the entire life of the people who live there. My parents, for instance, do not have a house decorated completely from items taken out of this year’s catalogs. Their furniture ranges in period from contemporary all the way back to Victorian. So a play about a similar English couple living in the Victorian period could have furniture ranging from Victorian back to Regency, or even Georgian.
When you study different period styles, you often run across lists and descriptions of what was “popular” or “in style” during certain time periods. Another idea to keep in mind is that most people are very varied in their stylishness. Some people always seem to be up with the latest trends; others have excruciatingly bad taste. During the Art Deco period, Ancient Egyptian motifs and styles came into vogue. That does not mean that someone would have thrown out all their furniture and decorated their place entirely in Egyptian-inspired furniture. Depending on how important style is to your character, there may be a few such pieces scattered throughout; there may also be none. Many of the characters in plays cannot afford to buy new furniture whenever tastes change.
Finally, I wanted to point out something which is obvious to many prop masters but not often to beginners. If your play is set in the 1920s, and you find a number of antiques from the 1920s, they will have a natural aura of age. Metal will have rust and patina, paper will be yellow and brittle, paint will be faded and peeled. This is not what the items will look like in the world of the play though. If a play is set a hundred years ago, that does not mean the items will look a hundred years old. Quite the contrary, the items will look new and well taken care of. A book will have bright white pages, metal will gleam and paint will be fresh. Obviously, the play itself can have antiques or old items; my point is that the contemporary props in a period play need to appear contemporary. For many props, you cannot use any but the most well-preserved antiques; you will have to find modern substitutes or construct your own.