Well then we wouldn't have been able to move to the Monday would we?
There actually WAS the exact restriction on conference dates I described a while back because a good friend of mine event managed a large conference at The Amex. Dates during the football season simply cannot be guaranteed. You'd think most Thursdays would be guaranteed but what if you got in the Europa League the next season or got offered another England U19 / 21? It might not be the case if you book one at short notice but rebook dates had restrictions on them.