True. As I stated though, I don't think as big of an issue for a US citizen. Can travel without getting a card renewed, less risk of being reported, etc. Worst case: even if it becomes rational later to renounce PR status (for whatever reasons), can still travel to Canada, even apply for nafta/cusma work permit, etc. (This may be a different situation for non-US folks in similar situation, as more dependent upon having an up to date and valid PR card - although I'd lean to saying possibly ok too, since the accompanying aspect less complicated - in their specific case).
Now I see your point: IF one knows exactly when one/both intend to move and there is some obvious trigger (kids' schooling, end of a longer-term contract, even retirement, etc), then sure: apply one year in advance to be sure.
But with staggered and uncertain contracts and kids as the poster states, I say forget trying to time exactly. (For those with permanent contracts - not as common in UN orgs as people may think - calculus may be different).
Again - I changed my mind because I think the circumstances are different (than generalized / assumed).
*A side note: this 'accompanying' thing seems to come up more often when one or esp both of the couple are effectively returning to their country of origin, for more or less permanent employment. (As noted, sometimes after very little time in Canada).
That is not the case here: this is more akin to a 'true' international deployment for both, in various countries - no hint of just using the PR status for convenience. Again, I lean to saying this likely works in their favour.
But yes: we cannot say how IRCC will treat in future. I still come out where I come out, on balance, things considered, etc.