Ah, if some broadcasters use different programme IDs for different seasons, that could well explain the problem. I thought it might have used cruder matching criteria like programme title (which has its own problems with false matching!).
Yes, both programmes are broadcast on the same channel.
I'll try creating an autorec separately from the EPG mechanism so it doesn't use the CRID and series link.
Just to make life more frustrating, I've also been making backup recordings on a dedicated PVR, but that seems to be deleting all the episodes from the list to be recorded after the first one has been recorded, even when I add them as separate episodes rather than as a series. That device seems to be very temperamental, and of course it's no longer supported as the maker seems to have pulled out of the PVR market and the URL given on its config screen points to a site in Chinese.
Apart from the series link problem (which I detected in advance of recording), and one episode that only partly recorded because TVH got into a silly mood and refused to write to the recording directory, even after several reboots, I've not lost a recording yet.
We're about to move house, and the house we're looking at seems to be in a small area (several streets that slope the wrong way!) that gets very poor terrestrial reception and it has only a dish not an aerial, so if we get that house I'll have to buy a couple of USB DVB-S2 devices and get to grips with how TVH works with satellite channels. That will be fun ;-)