Decennial ABC: D as in Deletions
In Wikipedia, anyone can create a new article. Consequently, anyone can ask to have an article deleted. It seems obvious that there have been no article deletions in traditional encyclopedias, because such articles would not have been written at all.
Only a few medieval works pursued after the year 1500. The knowledge in them was dated, new knowledge was extracted from scientific experiments. It needed shortening and actualisation to make these works suitable for the renaissance readership. 
As the encyclopedias grew and became multi-volume in the 18th century, they could cover more and more subjects. But from edition to edition, encyclopedias did delete or shorten old articles if they no longer interested the audience. When an anonymous printer republished Dennis de Coetlogon’s Universal history in 1759, he reduced the 169 treaties to 132. Above all, treatises with theological subjects were eliminated. 
With regard to Wikipedia, many outsiders don’t understand why an online encyclopedia has to delete articles. Web space is cheap. But most of them can accept the explanation that an article costs a lot of work. According to Kurt Jansson, the German Wikipedia pioneer, the question about relevance is in fact the question: how much does this subject matter to us that we accept the work it will cause the following years. Many articles are not up-to-date.
How will Wikipedia deal with article deletions in future? When article numbers rise and the community stays the same or shrinks, will notability criteria tighten? What is true for new articles, can also be applied to old articles.
 Robert Luff: Wissensvermittlung im europäischen Mittelalter. ‘Imago mundi’-Werke und ihre Prologe. Max Niemeyer Verlag, Tübingen 1999, p. 425.
 Jeff Loveland: An Alternative encyclopedia? Dennis de Coetlogon’s Universal history of arts and sciences (1745). Voltaire Foundation, Oxford 2010, p. 79.