Don and Linda..... Just to make sure you understand..... The $20000 credit limit is your personal credit limit. Everyone's is different based on their situation. Others are higher than that. I had mine increased by calling and asking as I knew I had some major purchases coming up. This is your credit limit, the amount you are allowed to charge up to in one billing cycle. This is not the number of travel reward dollars you can earn. In fact, with the correct Capital One card, you can earn up to 40000 points each billing cycle if you charge the full $20k and pay it off each month. Also, your points don't expire. The 90 day limit you referred to is that you can only use them to erase travel that has been charged in the last 90 days. You can accumulate points all year long, as many as you want, then use them to erase all the charges for one grand trip.
Not sure if that was your understanding or not, but just wanted you to know if it wasn't.