I think I have a work around: I just changed the file name in Windows Explorer and LR5 now detects it as a new file, so I can import it.
I'd still like to hear from others about this.
Is the original source for the tiff and jpeg files a raw file?
From the LR Library go to:
Edit >> Preferences >> General (tab)
Lightroom >> Preferences >> General (tab) on Mac OSX
Try putting a check-mark in the box to treat jpeg & raw as separate files. Does that make a difference?
That worked, it shows on the import now. (I still have to import it.)
BTW, original was raw (NEF) which I edited and it became a TIFF. Then reworking the TIFF and saving the JPG of that was where I was at. I still think LR5 should just catalog whatever the other editor saves but maybe there's a reason for taking on a TIFF and not a JPG.