Perhaps I can explain it.
iTunes downloads of Podcasts are based on the theory that when iTunes checks for new episodes (of your subscriptions), only one episode is new since it last checked. Therefore, that's the one that's downloaded. This works perfectly if one checks once a week - but only when there is just one new episode per week. Okay, check once a day (I hear you say). There is still an issue - some Podcast providers produce more than one Podcast per day.
Once a week: The Les Adams Podcast used to produce one episode a week (of his Saturday night show), titled "Dancefloor Classics". However, a while ago, Les Adams was given a second show, on the Friday, but this one is titled "Two Hour Takeover". So in fact it's two different programmes (same music, but different format), and I prefer the Dancefloor Classics show. But if I check for the Podcast once the Saturday show has been uploaded, a further anomaly appears because it's the Friday show that is automatically downloaded. To get the Saturday show, I have to manually click on the cloud icon. Since these particular programmes are removed after a week or so, if I forget to manually download the one I want, I lose it. And I'm not the only one to have this problem.
The Today programme (BBC Radio 4): This programme produces between two and four Podcasts per day - "Best Of Today", which are the short inserts they add into their morning programme. Each day, after the programme ends at 9am, they add some of those inserts to their Podcast feed. As I finish typing this post (at 10:35am), they have so far placed just one Podcast from this morning's show. Again, if one assumes that iTunes will download all of the episodes from one day, one is mistaken. Either, one has to manually click on the additional episodes, or your iTunes has to set to check every hour. Even then, that may not catch every episode.
I don't think the BBC even know there's an issue. Les Adams has had complaints from his listeners about this issue, but on air, he was at a loss to explain why this was happening. As far as I know, that's still the position today. One further point, you will notice that I say that it's the older episode of the Les Adams programme that is automatically downloaded. I haven't experimented to see if this happens with all Podcasts, such as Today programme, but I suspect that a previous update to iTunes has caused the older episode to download, rather than the newer one.
As I've experienced this problem for years, but been unable to convince iTunes that there is an issue (despite feedback to them), I've simply dealt with it as best as I can. Also, as I still don't have 8,000 points (despite contributing to the Apple forum for many years), I have no access to the forum Lounge, other members of the community or to other forms of feedback to Apple.