Mont. Code Ann. § 19-1-802

Nothing in this part may be construed to prejudice or otherwise affect any rights, benefits, or privileges heretofore accrued under any other law of this state. It is the intent of this legislation to permit supplementation of present retirement benefits under existing law with social security benefits. It is also the intent to permit teachers and staff in any district or institution of higher education so electing to become members of more than one retirement system, to receive credit under more than one system for the same service, and to receive benefits from more than one system. No benefits received under either system may be deducted from any other or separate system.