Well I've now played this 4 times. First time I got Bronze and knew that I'd do better so second I moved up to Expert and gave up after 5 years - I did make 2 mistakes - started railing too late so an AI also got into Edmonton and laid track before May so paid over the odds - but still
Third I tried (back to Normal) without any Industry - dismal failure
Fourth I went back to Industry for 6 months and everything went really well all through the scenario. Was able to manage almost without bonds after initial 4 to get started. At end kept selling my own shares to be able to buy the successful AI and took it over with a year to spare so was only left with loads from Athabasca. Didn't even get the minimum for Bronze despite using it as my hub with at least half my 60 or so trains going there
Don't know how you could ever get Gold carryings.
Incidentally in first few years the Almanac gave me Nil carryings from Athabasca despite my having carried perhaps 20 loads albeit of small value.
A hint - take a Bond immediately at start of game - if you leave it until May you'll pay 11% instead of 9%!
Anyway it's a really nice scenario and enjoyed playing it.