Dear Miss,
You may be correct about the word not having a plural form, but I have used it many times and confirmed by wiki-pasting a copy: etiquette (plural etiquettes). "The forms required by good breeding, or prescribed by authority, to be observed in social or official life; observance of the proprieties of rank and occasion; conventional decorum; ceremonial code of polite society."
Thank you,
Col Jude Mayne