That was probably the 12th supplemental to HT’s old TAA, done for the 2013 KX blockade. That would have been done under the old rules where you had to list all your diversionary routes in your TAA. Iirc, NR and HT did it under the Short Term approvals process so those rights, which would have been contingent in those days, died after the block.
In 2014 that all changed as a result of PR13 and the current rules were applied to all TAA. This is where you can go wherever you want on diversion, as long as you have route clearance and can be accommodated.