If you've been told by BA that they seem to think the very thing that you want to hear, I'd take that information with a pinch of salt. It could just be a technique to get you off the phone. If FTers don't have the definitive answer on a question as obscure and transient as this, the chances are that a BA call centre agent who seems to think X doesn't actually have the answer either.
Is there any known way to get them to honor their [perhaps misguided] promise over the phone? Are the BA Call Centre people capable of sending emails clarifying policy, or annotating my EC account, or something similar, so I can get back to them if [when] the Avios/TP's don't post and hold them to their word?