More information would help.
What version of Word are you using, and how are you updating your TOC?
If you're using 2003, and IF you're updating your TOC by selecting the
entire document (rather than just the TOC field), you'll re-set every field
to its default setting (which is probably blank). Try regenerating your TOC
by moving your cursor into the field and hitting F9. That "should"
regenerate the TOC only.
If that doesn't work, select the data in each text field, then right-click
in the field, select "Properties," and paste the date in as as the default
text for that field.
If you're using 2007, somebody else will have to answer your question,
because I haven't inflicted that problem on myself yet.
I hope this helps.
Fred