Sorry for (cross)posting this on another question already - I couldnt access your question yesterday - but just wanted to say:

To be honest, I think the best way, if you're in doubt, and have the luxury to do so: Take your carrier (empty) to the airport, and line up for checkin at your airline and ask the actual checkin agent about your carrier and their process. Be friendly, express your nervousness, tell them you got conflicting messages so you're instead there to ask an agent that actually would make such a that decision. If you're lucky, they would be sympathetic to your concern and tell you how they would really handle your specific case.

Just consider it a dry run.