Searching the Internet didn't turn up much. Some were discussing which template files to use. That would be the thing to check while developing the custom content type. But, I'd already made it past that consideration, because the code had been written months ago and was already well tested.
But, I saw a comment on one such posting: Go to the Permalinks settings and click SAVE.
I did, and presto the custom content type pages started working perfectly.
Process:
- In the Wordpress dashboard - navigate to Settings / Permalinks
- Click Save
That's it.
Apparently doing so will update your permalinks settings and flush rewrite rules. I suppose the process of bringing my site back to life caused unwanted changes in the rewrite rules. Initially Wordpress decided to disable some things because two plugins (including this one) were missing.