I think that the availability, or lack thereof, of BF upgrades can be tracked via the PDA website. Clicking on the upgrade standby list will list the number of BF upgrades for a flight. For example, today's flight 56 to CDG had 11 upgraded out of 34 booked (which was out of a capacity of 48, so presumable everyone on the wait list got upgraded).

I was listed on the upgrade site when I flew BF from NRT-EWR, which I used my WP miles to upgrade with.