I've just opened up my main panel with the plan of adding a new circuit, but have temporarily aborted that idea after squinting for a while, followed by getting worried.
I put some pictures from more angles at https://imgur.com/a/TZkSZQi.
There's quite a lot of 14/3 (or 12/3) wires running running in the top of the panel and fewer 14/2 (or 12/2). The double pole breakers at the bottom seem to be reasonable MWBCs to me, but I'm particularly worried about the ones I marked in red and yellow (a fairly large proportion of them!)
My admittedly limited understanding is that each full row of the panel would correspond to a leg of the incoming power, so MWBC should only share a neutral when they're on double pole breakers or otherwise spanning two rows by being part of a quad breaker.
So my questions are:
Should I be worried about the circuits I marked in red? They seem to have two problems: a) they're not tied but are likely sharing neutrals, and b) both hots are on the same phase, so possibly overloading the neutral.
Should I be worried about the circuits I marked in yellow? They aren't physically tied so the neutral could be unexpectedly live, but they at least seem to be on opposite phases.
I'm also in BC, Canada and the home was built in 2002 in case that's relevant.
I'm also still just assuming that the smaller gauge red/blacks are part of 3 conductor bundles, I haven't yet turned off the main power and started trying to deduce which white/red/blacks are going to the same place, but I suppose some stranger configuration is possible too. e.g. that the various 15A black/reds are indeed on opposite phases (though untied) but that's been accomplished by splitting across rows "manually" and keeping track of what's on which phase... somehow (could that have been Code in 2002?).
(Editing to add this pictures that shows cables, indeed, not conduit):