I've been tracking the "Z" bucket on a CO flight (in this case CO45 from MXP to EWR on Labor Day), since the BF summer sale began about a month ago. Well, that particular flight was Z9 for the longest time, and then today, I saw that it was at Z0. Is there any type of tracking log that I can access that can tell me the exact day it went Z0? In this particular case, I wanted to wait as long as possible (around Z3) before I bought a ticket, but I missed it.

Yes, I know that CO might put some seats back into Z, but that's not the point of this post.

The point here is just to see when exactly that flight on that date (4 Sept 06) went from Z9 to Z0. Does anybody know if/how to do that?

Thanks!