Ah ok, so going via the WLL/NLL is a 'Not London' route? I'd always remembered Kensington Olympia being on the list of London terminals...
Given that you must have been born in 1995 (or 1996) or you'd be on adult/YP fares, Kensington Olympia was removed as a 'London Terminal' before you were born! (
Source). It does seem odd that it was ever a 'London Terminal' as it would have meant that the 'Not London' fares for Cross-Country journeys would not have been valid on XC trains that went that way.
Anyway I'm sticking with my advice on the previous topic,
Alternatively Hook to South Hampstead +Any Permitted SVR (Child) is £15.15, which works out at 85p for each cross-London transfer, so this seems the best ticket to get.
I don't think there is any way to get the fare lower than that, I would be amazed if anyone can find a legitimate way to make it cheaper (but credit to them if they do!).
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Wrong I'm afraid, - there is no evening offpeak restriction out of Waterloo, only super offpeaks have a restriction.
You have it the wrong way round. It's not a case of saying there isn't a [super] off peak restriction for travel from a particular station. It's a question of whether there is a restriction from that station
for a particular ticket.
In other words, you
can't say "All [Super] Off Peak [Day] tickets are not valid at this station at this time".... well unless you have analysed the restriction codes for thousands of tickets to prove that is the case

!
For example, you say there is no off peak restriction out of Waterloo, are you telling me I can use an off Peak to Exeter at 1700? The restrictions suggest otherwise.
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I'm not sure what the validity of a Hook to London Terminals ticket is. Avantix Traveller has the text missing, and National Rail Enquiries also says it's
missing. I do know it's code US.
-
rjhglover says that the rtn portion of this ticket is not valid for leaving London between 1600-1900.
-
swt_passenger says the rtn portion is valid for leaving London at any time in the evening peak.
Can you both provide your source so we can verify please? That would be much appreciated

(and I'm struggling to find where the information is available so it would be good to know!)
What I can say is that Hook to
South Hampstead has validity code
2V, and the only restriction is that it is not valid before 0930 (no evening restriction at all).
I can also say that the East Coast site will happily sell an Off Peak Return from Hook to London Terminals, returning at any train in the evening peak. This suggests that
swt_passenger is correct for this ticket, but the general statement that suggests it applies to all tickets isn't correct, as the validity code does need to be checked.