We do some part checking when checking if a new subpart is added. 

This feels hacky, but it's placed here so that itaffects nothing else. We do a simple check to make sure that the subpart being added is being added to the part we care about.

Note that when parsing sections, this is done in the parser. We don't do this for subparts. It seemed like too big a change to change it now. 

An alternative solution would be to parse out the <REGTEXT> things out of the XML that we don't care about. But I feel like the day when we parse multiple regs at once from a notice is not far.