Roger, I have an 11x14 RC print on Ektacolor Plus paper from about 1980 mounted on a board as yours is and the matt board is glued to a stained wood frame. It is open to air.
The RC is showing no deterioration, nor is the color print. Of course, mine is color but then with all of the complaints about color, I just thought I would throw this in as an example.
I also have a number of 16x20s, mounted the same and on display at one of the local schools. These are a mix of color and B&W, and they are about 15 years old. No change there. Also, no toning.