Originally Posted by MarkXS

I highlighted the reason - it was right in what you wrote.
Airlines can SELL flights on airlines that are not alliance partners but with which they might have a bilateral agreement. AF->MA is that.

Airlines cannot do awards on airlines which aren't part of the airline with the miles (in your case, CO) award program.

It's not a distributive relationship.
CO->AF and AF->MA does NOT imply CO->MA for awards.

I'm guessing you could redeem AF/KL FlyingBlue miles for that MA flight, because AF partners with MA on that route. Just like I could redeem NW miles for a AMS-BUD NW codeshare on MA.

You had a free ticket using OnePass miles. You can only redeem on airlines that are award partners in the CO OnePass program. "Partner of another partner" does not count. By definition, any airline in the same alliance is an award partner. So any flight operated by a ST member is in theory available to you with CO miles (if it has award availability, of course). Also, as a CO member you have the ability to redeem on some non-Skyteam airlines that CO cut a separate deal with. You can redeem on Qantas and Virgin Atlantic from your CO program in Skyteam. I cannot from my NW program in Skyteam. That's because this scenario has nothing to do with Skyteam.

But now that I answered this, what the heck does your question have to do with the topic of the thread, which is about Copa remaining in Skyteam or going to *A?

To veer back on-topic, as a high-leve UA/*A elite and low-level NW/ST elite, I hope CO brings CM along for the ride. *A needs more help in Latin America than Skyteam does. CO itself will help a lot, but it would be nice to keep CM too. Though if ST wants to keep them, I'm thinking that their ST Associate status could easily enough be transferred to the New Delta and they would adopt SkyMiles (or SkyPerks or whatever it becomes) as their program, with a specially-negotiated one-time transfer opportunity for CO OP members who had earned miles on CM flights or who had joined via CM. This affiliation transfers for associates are not unknown; isn't one of the upcoming new ST associates originally sponsored by AZ but has been transferred to sponsorship through AF instead?