Notty will IN GENERAL pretty much kill out whatever else is in there, I hate to say. If lacto takes off early, it MIGHT have a small amount of sour. But, experience says that Notty will out-compete and kill off any lacto present. It is hardy and that's what yeasts do; kill off anything else by producing alcohol and they've been doing it for millions and possibly billions of years. That being said, some bugs don't really care how much alcohol a yeast produces and will out-compete them and take over a fermentation. This is where you start to hear "gusher" and "bottle bomb" from time to time. I'd wait until your gravity has stopped completely before bottling... And I'd give it at least a week between gravity readings and take 3 or 4 or even 5 in a row just to make sure. 15 points is a LARGE drop if that thing goes all the way to 1.000.
Were it my experiment, I'd probably take your cottage starter and ferment a small batch with only that. The results should be sour, tangy, and have a fair amount of alcohol in the end. It will probably be different if you wash the cake or even pitch directly onto the cake due to, in large part, what I said above.
One note; luck does play into this. If some bugs are just dormant and not dead, great things can happen. They can take off before the yeast really takes hold and you'll be surprised. It may be a good surprise or a bad one. If you've read anything on here about infections, you'll know what I mean.
Again, good luck.