Which then becomes a problem for hundreds of people when you hold up the line arguing with them about it. I'm not going to be that person who pisses off rush hour crowds over a point of principle. Far easier to just grab a transfer until they get it all sorted out.
And how about when the TTC switches to presto completely and there are no paper transfers, plus everybody with a metropass, token, or ticket is instead using presto? It is going to be an even bigger problem then, once they "get it all sorted out". If anything they should be MORE eager to check your presto card now that so few people are using them. And at any rate, interpretations of by-law 1 aside, if they give you trouble you can always call the police and press charges for harassment--additionally, if they try to somehow charge you under by-law 1, under some interpretation of the wording, no judge in the country will even HEAR that case, when the fare inspectors
have the checking device on their belt and
refuse to use it to check your fare!
Actually, looking at the fare calculator, I'm not sure. The example was from Exhibition, and I noticed they charged to Hamilton (or was it Aldershot, can't remember), rather than to Oshawa. But I'm just noticing (currently at least) that Oshawa is cheaper from Exhibition than either Aldershot or Hamilton. So I'll just say I don't know.
I guess it's an even bigger question from Union. Say you took the train to Oriole, the end of the line is $6.06 at Richmond Hill. But how do they know you didn't go to Kitchener ($16.38) or Niagara Falls ($23.09).
Bottom line is - I'm no longer sure what they charge - particularly from Union.
You're right, tapping on at Union, they would definitely not bill you to Richmond Hill, they'd certainly choose somewhere like Kitchener. However, I'm inclined to somewhat doubt they'd bill you to Niagara Falls--since that train is only seasonal+weekends, their system would need to be set up to only charge that as your final destination on certain days of the year; if we've learned anything about presto's systems so far, I think we can all probably agree that's too much for them. There's always the "let's screw customers over" mindset, of course, where maybe they bill it to Niagara Falls even on winter weekdays when the station isn't in service, just because it has presto readers technically, but I'm inclined to doubt quite that level of malice...incompetence, possibly, but I still doubt it.
I would be inclined to believe they would bill you to whatever the most expensive trip is excluding St Catharines or Niagara Falls--Allandale, Kitchener, or West Harbour, probably Kitchener if I recall my fares correctly. Also, if you call them, you could of course say hey, I travelled on a weekend, the Kitchener line isn't running, or West Harbour isn't in service, please at least just charge me to Aldershot; which I think would be a reasonable request and it sounds like they're flexible on forgetting to tap off. Or, of course, if you tap on to Viva at Langstaff, or MiWay at Port Credit, or whatnot--depends on whether that agency embeds location data, reasonably accurately, in their taps--that's pretty strong evidence you only went so far.
I think it's a bit of a shame that the system isn't built to allow a tap-on with YRT/VIVA, TTC, MiWay, a GO Bus, or what have you to double as a GO Train tap-off, but such is life. I've never forgotten, fortunately.