There is such a thing as a "grandfather clause" in intelligently written laws. The elephant that contributed it's tusks to the piano keys is long since dead. Also--is the customs agent competent to tell the difference between ivory and plastic or other materials?

The Brazilian rosewood tree that contributed to the back and sides of my guitar was felled many decades ago and contributed its wood to a whole bunch of quality guitars. Many years ago because the wood was aged for a number of decades before the luthier selected it for use in constructing a guitar.

Don Firth