I've been interested in this legend for a while because it leaves me with a lot of questions and has a tantalising feel of historicity. The detail in the title comes from these two paragraphs:

The earliest mention of the story seems to have been on a stained-glass window placed in the Church of Hamelin c. 1300. The window was described in several accounts between the 14th and 17th centuries.[8] It was destroyed in 1660. Based on the surviving descriptions, a modern reconstruction of the window has been created by historian Hans Dobbertin. It features the colorful figure of the Pied Piper and several figures of children dressed in white.[3]

This window is generally considered to have been created in memory of a tragic historical event for the town. Also, Hamelin town records start with this event. The earliest written record is from the town chronicles in an entry from 1384 which states: "It is 100 years since our children left."[9]

The sentence isn't contextualised any further so I don't really know how to interpret that. So how would historians approach that sentence? What kind of context should someone consider? Is a writer in those days saying "100 years ago..." more like saying "an indeterminate amount of time ago..." or more like saying "on the 2nd of August, 51 years ago...", ie. more suggestive than literal?

In other words, how accurate does the writer think they're being, and how do we conclude that?