Last week's 26th July episode is in HD with a rental expiring on 9th August so it looks like they are now made availabe in HD for 14 days after initial broadcast.
However if you search on TNA HD you will actually see further much older episodes listed as available in HD
Yeah the 14 day HD thing on YouView is daft, I'm pretty sure they're all available for longer on BT Vision Classic. From the dates of the old episodes in HD it looks like the deal changed at the new year for the YouView platform. Anyway, we normally get a new episode on Fridays and today's isn't up yet. I know they've had a busy couple of days