Or another way to sell papers. On a date of certain (good) historical significance, newspapers will stick in a supplement and declare themselves a "souvenir edition", although it's really just a normal paper with coverage of the event taking up a good ten or so pages. Examples:
- The marriage of a celebrity or perhaps a royal couple.
- The election and the inauguration of a new leader.
- New year's day, year 2000.
- Important national events like the Olympics.
- Local team wins a national title.