Longest alphabet in the world?

As it happens, it is Khmer. So says the Guinness Book of World Records, though just how many letters it has is unclear – 74 to 101 symbols, depending on how you count them.
This page gives the incredible magic number of 122 (33 consonants and 46 vowels=79 + 33 subscripts…wait, doesn’t 79+33=112?)
This page gives less – 71 (33 consonants, 23 vowels and 15 “ special vowels” )

I did try counting the ones available in Khmer Unicode and came up with the following tally:

35 consonants (two of which are obsolete)
17 independent vowels
19 dependent vowels (which adds up to 23 if you include composite vowels)
9 other symbols (one obsolete)

for a grand total of 84 characters (or 81, if one subtracts obsolete letters, or 77 if one subtracts composite vowels). Though with an alphabet this long miscounts can never be ruled out…