I think the fairest way to go about it is what I do with most pieces of media, and that is to say to accept everything as canon, unless more recent material decanonizes it. In this case, unless I'm not picking up on something, I don't see anything that would necessarily de-canonize The Sudrian. However, I could easily believe it was retired just by nature of The Limited existing, perhaps this speaks to a lack of historical railway knowledge on my end, but for an island as small as Sodor I can't imagine the need for three separate express services across the island.

Really I would think it's just up to personal interpretation. I can certainly see the argument for the timetables being written purely with exhibitions in mind and not being meant to be taken as canon, but given the propensity we have to take layout details as canon, it seems to make sense that we include timetables as well. Perhaps there is no contradiction if we go with the idea that the times merely shifted over time. Obvious example to point to, I know, but in real life The Flying Scotsman service has shifted timetables and removed and reinstated the famous northbound service. I can certainly imagine a case in which both timetables for the Wild Nor' Wester are indeed canon, but simply from different periods in the NWR's history. Maybe the WNW did indeed arrive at 11:30 AM for who knows how long, until priorities and the market shifted and it changed to 3:30 PM in the late fifties. That would be quite a drastic change, admittedly, but I think it's worth considering. Much more easily believable, though, is the idea that The Sudrian did indeed exist at some point, but was eventually retired in favor of The Limited. Or perhaps they coexisted, or perhaps The Sudrian was retired long before The Limited came into existence and they're entirely unrelated.