Well then, after a rewatch its really clear what the difference was. The first fight was reffed with a VERY "entertainment" ref style, the clinch broken almost immediately about 80% of the time. Reffing is huge shaper of Muay Thai fights for clinch fighters and the ref just took the clinch off the table. The belt fight reffed in a very different, traditional way (thank goodness). Also, Barbara didn't sink her head in at all in the August fight, which also added to the reffing issue, because Marie could get a handle for her various cross-faces and stalls, giving the ref something to respond to in his breaks. Barbara wasn't allowed to work out of those positions. In the title fight she sank her head in so beautifully, so adeptly on the grab, it completely eliminated the cross-faces and stalls. So, much more traditional reffing, and much better (in fact beautiful) entry techniques, and a hugely different result.
I'd also say that Marie was much more forward in the August fight, especially the first rounds, which kept Barbara a little off balance, instead of just seeking the rope with her back. It prevented, or at least deflected Barbara's stalking, where she's in charge of the timing of exchanges. Also, Barbara was much more proactive with her hands earlier, in the title fight, incorporating them into her stalking, which complexified the pocket.
But really none of these things were more important than the reffing, and the sink on the lock. Those differences completely transformed the result.