Although the tradition of giving themed gifts for specific year anniversaries dates back to the middle ages, those etiquette suggestions focus entirely on married couples. (see: History of Wedding Anniversary Gift Ideas for details) Why? There isn't any formal research, but my guess lies around the idea that dating relationships only took center stage for our romantic endeavors within the past fifty years, give or take. Prior to contemporary times, dating offered a means to get to know someone briefly before marriage, and rarely did couples date for extended periods of time.
Fast forward to today, where the majority of households house unmarried couples as opposed to married partners (U.S. Census Bureau. American Community Survey: 2005). Many couples date for years, and some specifically choose not to get married to their long term loves. Thus the need for some dating anniversary ideas and suggestions, such as: