Further, there's also the
contemp-notifier-last-updated field. Finding at setting that to something WAY in the future (like December 2500) would prevent this function from thinking that the theme needed updating.
The code suggests that the date is being stored in there as a Unix timestamp (instead of as a date), Depending on the type used the latest date possible might be 4294967295 (February 2106) or 214748364 (January 2038).
simple_xml_load_string line will be needed, because a text string is being stored, and the caller of this function will be expecting is XML.