Hi, Tim / Kevin,
For your information -- and for anyone else who reads this -- I finally determined what I was doing wrong.
When we initially made changes to the Framework, we knew we had to add the .dll with the new version number into the Global Assembly Cache (GAC). What we (I) did not get was that the current .dll must be added to the GAC each and every time we make any changes to it or we will not see the changes in behavior in the revised code because Visual Studio actually references the version in the GAC.
Once I remembered that step, things worked as expected.

Sorry for being such a pain in the neck.
Thanks for all the help, insight, and patience.

-Frank