Short answers, pulled from the story.
An anniversary is the date on which an event took place or an institution was founded. Most countries celebrate national anniversaries, typically called national days. These could be the date of independence of the nation or the adoption of a new constitution or form of government.
Emily Post published Etiquette in Society, in Business, in Politics and at Home in 1922. This work contained suggestions for wedding anniversary gifts covering 1, 5, 10, 15, 20, 25, 50, and 75 years. Wedding anniversary gift suggestions for other years were added in later editions and publications.
Silver marks 25 years in traditional anniversary lists. Pearl marks 30 years while Coral covers 35 years. Ruby reaches 40 years and Sapphire appears again for 65 years.
Swedish celebrities including Miss Sweden Johanna Lind Camilla Henemark Alexandra Charles and Christina Schollin celebrated the 100th anniversary of the birth of Mae West at Berns in Stockholm in 1993. Anniversaries of nations are usually marked by the number of years elapsed expressed with Latin words or Roman numerals.
The Latin phrase dies natalis literally means birth day. This term has become common in many languages especially in intellectual and institutional circles. It refers to the anniversary of the founding of an institution such as an alma mater.