If Yahoo! Autosync detects information conflicts like these, a window pops up saying “They aren’t synched, Here’s our suggestion:” You’ll see three:

1. Update to what’s highlighted—This option gives you the chance to check all the fields that differ to select which fields you want to keep going forward.
2. Create two separate entries—Click this when two contacts (or events, or tasks, or notes) are actually supposed to be separate instances.
3. Skip, I’ll fix this conflict later—Worry about it later. :o)