Permalinks being set to 1970

Hi,

Hope someone can help me out here. I’m building a family tree web site, and using the publishing date to separate posts by year so that the permalink reads, for example, /1967/gary-taylor/. This means my post permalinks all start with numbers, which is a Good Thing, I’m told.

This was working fine until I did one for my granddad, born in 1982. The start of the permalink is displayed as 1970, and Dashboard thinks that’s where it is too if I try and view it. However, the reference is correctly stored as 1892, and that’s where the post is located if I type the link in directly..

Same happens with my gran, born in 1898. Basically, anyone from the 19th century or earlier.

Edit: should also add that get_archives return the post years as 1892 and 1898, not 1970.

Any ideas?
Gary