I've recently been using the HTML validator provided by W3C to check these pages for errors. The TCBC site is not intended to be fully compliant, as it uses the non-standard but well-supported and sometimes essential <nobr> tag. Here is an external link explaining why this is necessary.

This page classifies each page on the sitemap in one of three classes:
Valid HTML 4.0 transitional  52%
Valid except for use of <nobr> tags  43%
Not valid—uncorrected errors  5%

As you can see, it's a lot less bad than it was. I'm working on it...