So if it substitutes letters which are not pronounced, what are those unpronounced letters in 'o and 'a? My guess is that they are a special exception which are always written 'o and 'a perhaps historically having had an official letter. If this is the case we could say the rule is:
lo + la + le (plural form) d''e also exists
A double apostrophe occurs when contraction is made with the definite articles, these being always written with an apostrophe.
So my further questions: a) Is there a "full spelling" for 'o and 'a?
it is not used - you only find it in veeeery old texts. nowadays they only use 'o, 'a and in plural form 'e
b) Are there any words besides 'o and 'a which take an apostrophe even when not part of a contraction?
yes - 'nfrumma,
'mbruglià
also there it substitutes a letter - in all cases the substituted letter is a vowel (as much as I have in mind now
and there's the article ll' used in front of a vowel
sorry, but things come in mind while writing and imagining sentences - consider that I know some grammar rules, but I don't know all of them - my Neapolitan comes from everyday use when talking with people in this region. The few rules I know help me to write as correctly as possible and according to Carmine who proofreads my texts they are quite well and getting always better - during the last ones there were only some really minor changes. If we need further, more exact information I need to find out where I can get a grammar book - it is impossible to find it here where I live (that might seem strange, but it is like that).
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