Turns out Johnny is Junie and Junie is Johnny.
S took a close look, and figured out that the cat we have been callling Junie on the assumption that she is a three-year-old female is in fact a male, and the cat we have been calling Johnny, believing him to be a one-year-old male is...female. We've gone back into the paperwork, and the mistake was perhaps made by the shelter, but could hinge on interpretation of terms like calico and tiger, given that they are both basically white cats with yellow splotches.
However, given that they have been neutered, and we have bonded with them as is, and they seem to be getting to know their names...we are now the owners of a one-year-old male cat named June Carter and a three-year-old female cat named Johnny Cash.
In other cat news, they are definitely out from under the bed, roaming the house, and quite snuggly. However, Junie has just started to scratch the sofa, which makes me not so happy. But S is getting a scratching post today (and I am trying not to think about the fact that our last cats disdained the scratching post and preferred the shelves of records, which is why all our records have shredded spines).