Correct me if I'm wrong: my interpretation is that the +1 episodes are being scheduled as previously missing, and the multiple recordings are treated as OK because they are outside the 3-hour window. Broadly the EPG is so cocked up schedchk can't deal with it.
I think you are correct - this situation is way outside schedchk's, the webif's and possibly the Humax's comfort zone
The Humax schedule database, webif and the rule books treats split recordings as a third type of recording that is neither one-off nor series, it should not be possible to have a series of split recordings. But logically that could be perfectly sensible - A broadcaster might wish to schedule Lord of the Rings as a series of three programmes each of which is a split recording. I have never seen that happen for a film series and this is the first series of "split" recordings that I have come across.
In this case I don't believe they are genuine split recordings, they are more than 3 hours apart, each half is identical length and can you really imagine 2:30 hours to describe building the Cutty Sark! So I think it is a broadcaster error to include the #01 IMI in the crids.
Normally if a series is to be repeated in another time slot it is given a different series-CRID so that you can choose whether to record the 13:00 or 18:15 showing.
PBS America+1 doesn't appear in my EPG since I don't receive COM7 but is it using exactly the same series Crid as PBS America? If it is that would explain the "Unscheduled episode" messages - another broadcaster error.
While duplicating an episode within a series-Crid is not common it is not that unusual either, I have seen it, for example, with the Simpsons on C4. The Humax avoids duplicate recordings by checking the already recorded list in the schedule entry and not re-recording the episode.
It will be interesting to see how the Humax treats Clydebuilt - if it handles it like a normal series it will automatically ignore the second showing, if it treats it as a split then it will record both.
The big problem with duplicate episodes is in resolving conflicts there is no way of telling the Humax to record the 18:15 showing instead of the 13:00, our normal way of skipping an episode is by marking it already recorded which would also stop it recording at 18:15, You would have one-off recordings for every episode.