When did coral start to be incorporated in Navajo jewelry?

Hello…I purchased a set of sterling watch tips a couple of years back with no marks of any type that I could find. The consist of one turquoise nugget & a piece of coral. I didn’t pay a whole lot so I’m not real concerned about their value but I am concerned about their authenticity. One of the pieces of coral has lost ALL it’s color & the other one is still bright red. I would like to be able to date these pieces…would they possibly of mexican origin?

Also, why would 1 piece of coral bleach out but the other one didn’t?

Thanks in advance…billgr0248

the coral could have been dyed? can you send images?