>>>They're consuming everything they spend. The purchased shares are being cancelled and the money is gone.<<<
Sorry, but I have to disagree with that line of thinking.
Buying back shares is simply paying off a debt. The share holders are entitled to the spot price of the shares whenever they choose to redeem them. When earnings, cash flow, or anything else is divided by outstanding shares the cash will all reappear like magic.
As we all know, the true measure of the buyback is the future share price. Management is in the best position to guess what that might be.