To give an example from Zone 2 Site 6 (Ottawa):
You might expect 142.890 to be paired with 138.870, which it
was when it was a conventional MOH pair, but the input is now 149.830.
138.870 is (was) paired with 142.515 output, which is no longer
used on this site.
You might also expect 142.335 to have input 138.315, but its input
is 138.375; 138.315 is paired with 141.690. And so it goes.
Hydro-Quebec uses 142.395 which you might think goes with 138.375
(above), but Quebec and some other provinces typically use 3.99MHz
separation rather than 4.02MHz, and again there are lots of exceptions.
Dave