Often (and I don't really know) the imported file will have a date such as 1614/1615 or 1614/5, indicating old and new style. The wiki machine can't read this number so it drops off the last portion and posts a note about it can't interpret the number.
In reality, the new style date always takes the later year because the change involved both skipping over eleven days and changing new year's day from Mar 20 to Jan 1.
We should just bite the bullet and accept the second year and forget about the difference, but for some reason there is resistance to this. IMHO.