I don't know, sorry Andrew. RONSKI and wombat may remember
Packages using 80/20 speeds may have become available formally in Spring 2012, I'm not sure of the exact date. Plusnet ran a trial with those speeds, which meant mine upgraded in February 2012, but I don't know how things went for the general public.
However, the cabinets were converted to the 17a profile in Autumn 2011. IIRC, the process was gradual.
My old line was affected by this profile switch... on the 8c profile, my old line suffered from errors and packet loss, and DLM intervened to drop the sync speed from 40Mbps to around 37Mbps. However, on the switch to the 17a profile, the adjustment to the frequency bands allowed my modem to sync at a full 40 without DLM intervention and without the errors & packet loss. That happened when the profile was switched in 2011, months before 80/20 services became available.