Eric, the index to Animal Comics on the I Go Pogo website is part of a much larger work covering all of Kelly's comic book work published over several issues of The Fort Mudge Most, a fanzine published by the Pogo Fan Club. I wrote those articles and compiled the index, which was pretty much just my eyeballing all known Kelly comics. In the course of the articles, I found what looked like a couple of new stories and refuted some others. But it was all just my opinion, no data to back it up. Steve Thompson of the Pogo Fan Club says he has discovered some work payment receipts among the Kelly family papers that may shed some light on what exactly is or is not Kelly. But until that list is made public, we're all on our own.
The Purpose of the Porpoise does definitely look like Kelly (how did I miss that one? I'll have to check my original index!), but I would still say no to The Donkey's Dilemma and The Magician's Rabbit. There were many artists with similar styles doing the same comics at the same time. The hardest to spot are the Kelly covers on Walt Disney's Comics & Stories, where nearly everyone was using the same style. I hear Carl Buettner is the artist on some covers that seem to be obviously Kelly. Then there's the possibility that Kelly pencilled and someone else inked, making it unrecognizable.
Towards the end of the 1940's, Kelly's work got so heavy that he began employing assistants. Their work is most evident in most of the Pogo Possum comics where the style varies wildly from one story to the next. This is just a long way of saying, "your guess is as good as anybody's."
But my real reason for writing is to thank you and the others that are making all this Kelly work available to fans this way. Despite the reprinting projects that have happened erratically over the years, so much of Kelly's work has been overlooked and forgotten. This is probably the only way to keep the Mother Goose and Fairy Tale comics available to a new generation. (Not to mention all the other Golden Age greats that nobody can find or afford any more). Thanks a bunch!