I solved the problem. I failed to fully understand the interface for saving memory changes. In my opinion, the root cause is a VMware Fusion user interface bug.
SOLUTION:
Memory changes are NOT saved if the user closes the Processors & Memory settings window without going elsewhere in Settings first. (You close the window by clicking on the red button in the upper left corner of the window, or by pressing Command-W on the keyboard.)
To save changes to the Memory setting in a Guest OS, you must click the back (<) button or the Show All button at the top of the window first. Then you may close the Settings window. If you follow this two-step procedure, then changes to your Guest OS Memory setting will be saved.
COMMENTS:
I will try to report it as a bug to VMware. This user interface design is wrong; it is not intuitive. Other settings are saved when the window is closed, including the Processors setting, which is on the same panel as the Memory setting.
When I made memory settings changes in the past, I must have gone back into the main Settings window to make other changes before closing the settings window.
Thanks to everyone for their suggestions. It would be helpful if you could confirm that this same bug appears on your systems.
P.S. Anyone know how to file a bug report with VMware?