Chalk this one up to goofer error combined with what is a minor bug! ;)

Apparently, when compatibility mode was invoked, the worksheet was expanded
to larger than the display/visible area. There was no way to scroll down to
click on Sheet 1, where the data was.

I was able to shrink the sheet from the upper right corner until it was
small enough to move back up, finally uncovering the hidden Sheet "n" tabs.