Why are the dates different?

You will notice that the dates that I give for Henslowe's entries are often different from those that he actually wrote in the Diary.

It's generally believed by scholars that the dates in the diary are frequently muddled. For example, he often lists performances on dates that were Sundays, which was against the law. The dates in the diary typically snap into sense if one assumes that Henslowe got himself a day or two out of sync while writing the entries. Often, one can see a small error of dating being perpetuated for long periods. 

It might seem odd that Henslowe would not notice these errors, but most scholars think he wasn't actually writing these entries one by one on a daily basis. He was entering the data some time after the performances, probably writing multiple entries in big blocks, and that made it easy for dates to be misremembered.

An additional complication is that Henslowe uses the old style of dating in which the new year begins on 25th March, so dates before then still have the date of the previous year.

In correcting Henslowe's dates, I am indebted to the work of earlier scholars (especially Martin Wiggins in his Catalogue of British Drama).