Hi, Kate,
I don't know how the TOC field works internally, but it appears that it
won't hyperlink to files other than the one containing the field. At least,
I couldn't make it work with RD fields.
An alternative might be to use IncludeText fields instead of RD fields.
These bring the actual text of the linked files into the main document, so
the hyperlinks work. The penalty is a large, unwieldy document.