Puzzle ZSGJ

A 'complete' word is a word in which every letter, in turn, can be replaced by another to form a new word.

For example, RUG is a complete word because:
   -ug = hug
   r-g = rig
   ru- = run

How many of the following words are not complete words? Proper nouns and names are not allowed.
hard port duck bugs bail mast thin lean fire read

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Hint
Another example, PEN is a complete word because:
   -en = ten
   p-n = pin
   pe- = pea

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