An attorney would need review the CC&Rs and have a lot more information to be able to answer your question.
For example, was the HOA board's approval of the composite roofs all given at the same time, or was the composite roofs the original roof which the CC&Rs later prohibited? Did the same HOA boards approve the 14 that have the composite roofs? What was the stated reason for denying your request?
CC&Rs would need to be consulted.
If the HOA had notice of the composite roofs and took no action against it, the HOA could be viewed to as "waived" their right to enforce the "non-composite roof" policy. In any event CC&Rs need to be reviewed and the specific circumstances of the existing composites and their timing need to be reviewed.
Let me know if you need any further help.