When the Arsenal game was postponed 11th March 2020 the club did say all Ticket Exchange sales would be honoured however that ST Holders who wanted to go would be able to have first dibs on any tickets at ST prices.
We don't know how the above would work as it never happened, and there were a lot selling as the fixture was only confirmed on 4th March 2020, City were not in contention in the league, and there was likely to be slack when rearranged.
The club also want it both ways, if someone buys your ticket/s and cancels with a few days to go (happened last season a lot when the club reduced all prices to £30 and people rebought) the club denies it was ever sold even though they told you it had and it showed as sold in 2 places on your account, and it becomes your liability at short notice. When raised as an issue with the club it doesn’t get past the front line.
It will be a mess as those who bought tickets from the club and exchange will wait for the new date, then a lot will cancel, and quite a few more will want to sell, and there is no online way to cancel a ticket to a rearranged game. Plus the buyer can still cancel until the last week, so even if you sold, and wanted to sell, you could be lumbered at short notice. Without a clear written policy what could go wrong?