Bumping this old thread because I just did some tax-loss harvesting with partial lot sales in my Vanguard brokerage account.
I sent my rep a secure email telling him which lots I was selling for specific id. I didn't expect a response back -- I figured I was just covering my butt for the IRS and would do the accounting myself.
But I got a response back. My rep told me "done!" And it turns out that he annotated my online realized cost basis info with the requested lots and acquisition dates.
Cool -- does Vanguard do this consistently, or am I special?