In that previous thread with the "critters" I collected (What species of salamander larvae are these? And, how do I keep them when they "grow up"?
), I got lots of suggestions and from here, zookeepers at the zoo where I volunteer, and herpetologists at Michigan State University and Eastern Michigan University. I think I finally have an answer, though.
I heard on this amphibian internet board/forum (caudata.org) that Tiger Salamanders have "yellow" bellies. I just looked the three species that were suggested by people on the internet, including you two. The page http://www.mass.gov/dfwele/dfw/nhesp...a_laterale.pdf
says of the Blue-spotted, "A dark blue to black dorsum with brilliant sky-blue spots or specks on the lower sides of the body makes the coloration of this species quite distinct and reminiscent of antique blue enamel pots and dishware. The ventral surface is a paler grey with black pigmentation surrounding the vent". According to many pages, the surface of Spotted is "slate-gray" or "gray". I've seen the belly/ventral side of this salamander, and it definitely dark yellow, not gray, slate-gray, or paler grey (gray)/black.
Very unusual for larvae to mature at the approx 2.0 inch size. According to Harding's book Amphibians and Reptiles of the Great Lakes Region, larvae can transform at sizes as small as 2.8 inches, but J. Alan Holman's most recent (posthumous) book, The Amphibians and Reptiles of Michigan: A Quaternary and Recent Faunal Adventure, says they can metamorphose at as small of size as 1.93 inches. Since this pond's standing was was very small, almost gone, they probably had "pressure" to metamorphose at a very small size.