[RichardJ]

My bad typo in the example - $lng.lbl_Customer. It is actually $lng.lbl_customer.

No misspellings in the actual code.
Cleared template cache using the Summary/Tools/Clear templates cache operation
No better results.

So I backed up the templates_c folder (just in case) and deleted the contents.
Voila! all the labels are displayed.

Now to check that I broke nothing else... heeh!

Thanks for the pointer. Much appreciated.