but why is the Iver split valid for trains not stopping at Iver?
Because one of the tickets in the split is a Season. As BandHcommuter says, it matters not how many tickets are used to make a journey. One (and one only) Season in the combination and a journey on through trains from the origin on the first ticket to the destination on the last ticket can be made without having to call at stations where the splits are made.
I recently travelled from Plymouth to Swindon via Reading using the following combination:
- Plymouth - Tiverton Parkway, return portion of an Off Peak Day Return.
- Freedom of Severn & Solent 3 in 7 Rover (This counts as a Leisure Travel Pass for the purposes of Condition 19(c)), valid Between Tiverton Parkway and Westbury
- Westbury - Theale, Super Off Peak Single
- Theale - Cholsey, Off Peak Day Single
- Cholsey - Swindon, Off Peak Day Single
My first train from Plymouth to Reading didn't call at Tiverton Parkway or Theale. The second train didn't call at Cholsey. No problems encountered using that combination.
The original purpose of Condition 19(c) was to allow Season Ticket holders the same right to extend their journey as a holder of a normal ticket. Normal tickets can have their destination changed by means of an Excess Fare. After the excess the ticket becomes a through fare to the new destination with no need for the train you are taking to call at the original destination. Season Tickets can't be excessed in this way for individual single or return journeys, so the only option is to buy separate ticket(s) that abut the Season Ticket and give the holder of the combination the right to travel on trains that don't call at the stations where the tickets abut. Further individual single or return tickets can be added to the combination that don't abut the Season. Thus we have Condition 19(c).
That condition can then be used advantageously to save money in certain circumstances, such as those I've highlighted.
Within the spirit of the condition? You could argue that it isn't.
Within the wording of the condition? Absolutely. And therefore allowed.
If you're not comfortable using Condition 19(c) in such a way, then of course you can do a 'normal' split as per Condition 19(b). But that will limit your options to trains that call at the split points.