I'll ask about this, but I suspect it needs to be used with the expectation that at least one of the origin/destination is outwith the area of the pass to get sensible results. I'd expect similar results for Watford Junction on LO services. Ideally, I suppose it would simply refuse to provide any fares under these circumstances.
Thanks - I note with other examples where I enter 2 stations within the 60+ oyster area (e.g. Charing Cross and Erith) I get the error message
"Sorry, an error has occurred.
Boundary zone searches need to be between a zonal and non-zonal station".
which seems sensible.
My suggestion is that the journey I have detailed also needs to show this same error message.
I'm speculating a bit here since I obviously don't know what is going on "under the bonnet" with the trainsplit engine, but the difference appears to be that although Dartford is definitely in the 60+ oystercard area, it is outside of Zone 6. As far as I can see, Dartford is the only station outside Zone 6 not served by a TFL service that is in the 60+ oystercard area, so is something of an exception which is not being recognised by trainsplit.
It does raise the question as to why this exception for Dartford? Again guessing a bit, but could the rationale be to allow people travelling between stations on the southeastern metro lines (Sidcup, Bexleyheath, Woolwich) to be able to travel via Dartford rather than central London when using the 60+ oystercard?
By the way, I don't envy you guys at trainsplit attempting to code all of these rules, and well done for being the only site (that I'm aware of) that attempts to handle this
. I hope you don't mind me highlighting some of these issues.