Regarding the OP, those are a later production run of the Baltimore Aquarium frogs set. The Lehmann's Poison Frog also saw it's legs and toes get thicker later in the production run. I always assumed that they were the result of mold degradation and necessary adjustment. The original figures in the set had slender legs and delicately sculpted toes. The later figures, with thicker legs and toes, also were cast in softer vinyl than the originals, and the green-and-black poison dart frog got a greener (less minty) paintjob. Later still, the Yellow-and-Black Poison Dart Frog and the Lehmann's Poison Dart Frog both got white toes, for reasons unknown. They were all still released under the umbrella of the Baltimore Aquarium collection. I'm pretty sure the thick-toed figures appeared around the same time as the Red-eyed Tree Frog was added to the collection. *Note* The Red-eyed Tree Frog was sold in a "Rainforest Frogs" collection box with the other figures in the collection, and was also available loose, just as the other figures were. I think that the thick-toed figures were sold loose; I don't know if they were used in the Rainforest Frogs collection box.
Finally, the Incredible Creatures Poison Dart Frogs introduced updated, albeit less detailed, sculpts and paintjobs (and dropped the Lehmann's and histrionicus species in favor of Oophaga pumilio red morph and Blue Jeans morph). These Incredible Creatures Poison Dart Frogs were sold loose or in sets (marketed as Point of Sale Bin Figures), and finally, they were put into the Poison Dart Frogs TOOB (where they introduced the Golden Poison Dart Frog and Sira Poison Dart Frog).
So to end any remaining confusion, you have an early version and a late version of the same Baltimore Aquarium Collection Green-and-Black Poison Dart Frog and Yellow-and-Black Poison Dart Frog figures. The earlier, and IMO. superior, figures had very delicately sculpted toes and slender legs. But there wasn't any real differentiation between how they were marketed or sold.
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Though, I want to share here again a catalogue scan I received from Safari at that time. It explains why half of these frogs have different release dates and also the archaic product numbers. I've found also that Andreas frogs are marked 1990 and that's one of the misteries because those are the ones with thick toes. I confess sometimes it looks like there are three versions, thin toes, thick toes and very big toes but it is hard to tell from some angles and I don't want to get it more complicated.