These are the steps, and my progress through them:

• DONE: Start with MdhRecordList, and ensure that nothing can set the value of $parentSuffix to anything except an empty string. Test thoroughly.
• DONE: Next, move to MdhRecord, and ensure that nothing can set its $parentSuffix to anything but an empty string. Test again.
• DONE: If all is well, eliminate all uses of $parentSuffix from MdhRecordList and test again. This will leave the class making calls to MdhRecord methods where it supplies an empty string in place of its $parentSuffix.
• DONE: Identify those methods in MdhRecord, and refactor them so that they don't require that parameter; then remove it from all calls to the methods. Test very thoroughly.
• DONE: Remove all remaining code from MdhRecordList which references $parentSuffix, and test again.
• DONE: Remove all code referencing $parentSuffix from MdhRecord, and test again.
• DONE: Examine gui.js. This has functions which look for the parent suffix and use it (although I believe it's always an empty string) to build ids for form elements and querystring parameters. Remove all references to it, and test again.
• DONE: Look at get_rec.php and save_rec.php to see if mentions of suffixes and ids there can now be simplified.
• DONE: Test test test test...