I'm very grateful for this question.....because I had no idea the plural for lettuce was the same as the singular - although thinking about it 'lettuces' does look a bit weird.
That said, I only found out recently that blonde and blond are different!
I remember the sugar shortage. My cousins used to have three teaspoons in their tea until their Mum offered to stir it for them ' No Mum it tastes horrible' - they just liked the sugary sludge at the bottom of the cup when they'd drunk the tea.
I won't lose any sleep at not being able to buy iceberg - horrid watery tasteless stuff, yuck.
Donkeys years ago some researchers in California declared lettuce to be carcinogenic - do be careful, gromit! I believe it is rather nice braised (honestly) but I've never tried.