This PmTcaUnsigned64 is a frozen snapshot of cienaCesPmAdjustmentTcaBasisValueMax exactly as it stood when the last end-of-interval Adjustment TCA occurred, per its DESCRIPTION. This is the ceiling-side mirror of the BasisValueMin snapshot, preserving what the basis's permitted upper limit was at that historical moment so you can tell, in hindsight, whether that old TCA happened while the basis was already pinned at its maximum. For example, seeing this snapshot equal to the LastIntvlEndTcaBasisValue recorded for the same event tells you the basis had already capped out at its ceiling when that particular TCA fired, consistent with a recent capacity upgrade having just maxed out.