Great-glassuk states that Arabia took over Nuutajarvi in 1971, and Kahula-Iittala took over in 1988. But when/whether they stopped using the brand is another question, as you know!
The brand name must have been phased in over some time, starting with glass export and then moving on to the whole production, according to the little insert I found with some bowls which came in the Nuutajarvi box, but with Arabia labels.
Here's the text, in case you're interested ('Scuse typos!):
The beginning of a new era. Our old mark with be changed into: (...there's a logo here, ed followed by the words) Arabia, Wartsila, Finland.
From now on, Notsjoe glassware will be called Arabia glass. For technical reasons, these glasses still carry the old (fish) symbol. The change of name will make our ever-growing exportation easier. We have already used the name Arabia for exports because it is a very well known name all over the world. Besides, Notsjoe is quite difficult a name to pronounce in many languages. That's why these glasses, too, are now Arabia glass. But as before, they are made at Notsjoe Glass.
Ivo, would a picture of the bowls, packaging & labels help to narrow down dates?
Does any of this help?
I've edited this to take out the stuff you must know already, Ivo!