I checked your gallery to try to find out what kind of images you're talking about, but can't see any that looks like multiple exposures.
Do you mind sharing what kind of pictures you're talking about? The few multi exposures I've done have been such experiments that they could just as well have come out as jpegs.
I haven't checked up on the Multiple Exposure feature of newer Canons, but I remember testing one of the first implementations several years ago, and the camera was not allowing multiple exposures to reduce noise, because the camera always ran NR on the existing stack before adding another image, it seems, as the noise seemed to be the noise of a single photo, with none of the reduced noise expected with stacking. I found that very disappointing.
The reason noise usually reduces with stacking is because the positive and negative noise "errors" from various frames cancel each other out, and cancel more, the more you stack, but if you smooth the existing images first, there is nothing in the existing stack to cancel any noise of the added image. This is a bizarre situation where NR actually INCREASES noise!

And they are oftentimes crazy!

