It is only likely to have been from the Rosenthal range if it is very finely blown, rather than a bit chunky.
I love these vases/bottles. I reckon the way the blue is applied is in a manner very similar to the way the wing casings of fish vases are applied, but rather than being made into a lumpy feature, are blended into the body - you can see that each side of the vase has been dipped, and there is the "strap" across the the middle, between the two side casings, as the vase is lifted and turned, to catch the strand that falls.
This one is the first I've seen that is later than Michael Harris, and I'm pretty sure nearly every one I've seen has Michael's signature on it. It's a very accomplished piece. The Boffos were gone by '73, so it is very likely by Joseph or Paul Said, as I believe they were the most accomplished glassmakers there at the time, having been the earliest apprentices.
I have also been told that Paul Said never, ever signed anything.