Mich. Comp. Laws § 700.2952: Validity.

Sec. 2952.

If a will is made in the form of an international will that complies with the requirements of this part, the will is valid in regard to its form irrespective of the particular place where the will is made, of the location of assets, or of the testator's nationality, domicile, or residence.

A will's invalidity as an international will does not affect its formal validity as a will of another kind.

This part does not apply to the form of a testamentary disposition made by 2 or more individuals in 1 instrument.