From International Robin Hood Bibliography
When I write an introductory page to Allusions, I must remember to say that I have used the date 1500 for allusions dated "late 15th century", 1600 for allusions dated "late 16th cent. etc. This was done to avoid seriously complicated code for the navigation links (L15c should come before 1602, but only if there are no L15c items after the one in question). Assigning a proepr year is also the only way these allusions can be included in statistics based on year of writing. For early 15th century I must use the date 1401, for mid-15th century the date 1450.