What happens when you start Thunderbird? Does the new account wizard come up?

It is highly unlikely that your problem is related to the update.

The account wizard requested data that I supplied, then Thunderbird opened to my preferred default tab of Calendar View. Only calendar that then displayed was a blank “home” calendar, with none of my previously available eight calendars being accessible for displaying. Tried first solution found at: https://support.mozilla.org/en-US/kb/calendar-updates-issues-thunderbird without producing any observable results or consequences. The application updates appear to have replaced Firefox and Thunderbird/Lightning rather than simply updating the applications, although I find Thunderbird add-ons previously installed remain present. Thank you for your interest and endeavors. _George

It seems Thunderbird lost track of your existing profile (for whatever reason), and started with a new one.

Follow the instructions below to navigate to your 'Profiles' folder. http://kb.mozillazine.org/Profile_folder_-_Thunderbird#Windows_Vista.2C_7.2C_8.1_and_10

Please post a screenshot with the 'Profiles' folder selected in Windows Explorer showing it's contents.

My old and new Thunderbird profile contents are attached.

I was more interested in one level higher, i.e. the contents of the 'Profiles' folder.

Are there any other profile folders than 'eaascz68.default' and '_(old)_eaascz68.default' ?

You'd also need to explain what 'old' and 'new' profile means, how you got to '_(old)_eaascz68.default', and why.

There are two files in the Thunderbird folder named “Profiles”:

1. The file eaascz68.default was newly created upon restarting Thunderbird following the instructions in the remedy offered at: https://support.mozilla.org/en-US/kb/calendar-updates-issues-thunderbird

2. The file _old_eaascz68.default is the sole prior existing profile (eaascz68.default) that the above mentioned instructions suggested I rename to disable and preserve it prior to rebooting to create a new profile. It was my choice to rename that prior existing file by appending the descriptive term “_old_” to give it the name _old_eaascz68.default.

Attached is the screenshot “up one level” you requested.

1. The file eaascz68.default was newly created upon restarting Thunderbird following the instructions in the remedy offered at: https://support.mozilla.org/en-US/kb/calendar-updates-issues-thunderbird

I'd be curious where in the article is stated to create a new profile. Can you elaborate on which instructions you followed, and what exactly you did?