Thanks, LorenzoGatti. I didn't quite understand what you were referring to and am still too ignorant to know if you were telling me the answer but you did send me down a path of investigation which resulted in a fix.
Anyways, I have made the problem go away. I believe the problem is related to the build order of the jar files. When I put "common.jar" at the top of the compile list the problem goes away.
My ignorant theory:
common.jar is used in many other jar files. Many of those other jar files are also included in the problem file, "detroit.jar". When I make a change to common.jar it isn't being seen by detroit.jar because an earlier .jar file has already been compiled which includes the non-editted version of the classes in common.jar. It's this old version of the classes in common.jar that are being seen by detroit.jar. The class is there but the new method is not. New classes and methods are seen but new methods of previously existing classes are not.
Odd thing is, after moving common.jar to the top of the compile list, compiling successfully, then moving common.jar to the bottom of the compile list, it still compiles fine so there's some understanding I still don't have here. I can duplicate and resolve the problem at will at this point by adding new methods.
So, other than ensuring common.jar is always at the top of the compile list, is there a better way of avoiding this problem?