Today — May 8 — is one of two possible dates for commemorating the anniversary of Julian of Norwich’s revelations. They took place on either May 8 or May 13, 1373. We’re not sure which, because the oldest manuscripts contain both dates. Obviously, at one point a scribe mis-copied the date, and of course we have no way of knowing which of the dates was originally recorded in Julian’s own hand.
The error makes more sense when you recall that in the fourteenth century, numbers will still written using Roman numbers; so the conflict is between May VIII and May XIII. Somebody at some point was a little sloppy in making a V look like an X (or vice versa), and then the error crept in — to at least some of the manuscripts.
As far as I’m concerned, all this means is that we may as well honor Julian’s visions on both the 8th and the 13th!