The assets of the retirement system shall be invested and reinvested without distinction as to their source in accordance with § 67, Article XVI, Texas Constitution. A determination of whether the board of trustees has exercised prudence with respect to an investment decision must be made taking into consideration the investment of all assets of the trust or all assets of the collective investment vehicle, as applicable, over which the board has management and control, rather than considering the prudence of a single investment of the trust or the collective investment vehicle, as applicable.