Yes, it can be very frustrating. The big thing to remember here is that it is the operating metal and fare class that determines what you get. The big mistake is to assume that the code you see for the codeshare flight maps directly to the same code on the operating carrier.

Take the first example above. Let's just say you purchased the ticket on the CO website that had a CO flight number but was operated by AC (looks like it would be a 3xxx flight number). Let's just say that was a flight between the US and Canada and an S fare. That S fare on CO could map to G on AC (no ROP credit), or W (100% ROP credit). The mapping usually isn't known so it really could go either way. There probably is a method to it, but us on the outside just don't know what it is. The best we can do is use anecdotal evidence. In your case it mapped to a fare class that earned miles.

I'll say again, this is exactly the reason why Flyertalk rule #1 is avoid codeshare flights whenever possible. It can also affect other things besides mileage credit, but that's a different story. While more time consuming, if one see's the situation in the first example, the best thing to do is to try to find the same flight with an AC flight number. That way it usually is unambiguous. Obviously there's always exceptions, but at least I have noticed that I get what I expect when I avoid codeshares.

And I'll also completely agree about streamlining the earnings among the *A carriers. It would make things much easier to deal with. But the system is what it is, and once you learn how to play within that system the headaches become much less frequent.

Hopefully that little ramble was useful.