US Bank, Colorado Creative, ad hoc check holding Internet

1. US Bank held the check and then released the funds. Did I mention they were no longer pending? Did they not find out then that it was from a closed account? If not, what was the purpose of "pending" deposits?

  You're right.  They released the funds and they were no longer pending.  The purpose of pending deposits is to hold funds until they can clear.  Unfortunately, Regulation CC (Expedited Funds Availability) says the bank can only hold onto funds for a given period (complicated rules depending on the check).  The bank must release the funds even if the check hasn't actually cleared.   Just because the money shows up in your account, doesn't mean the check cleared.   The bank can be fined if they don't release the funds, regardless of the status of the check.

2. They released the funds, and the burden of checking the client's bank is not on me. The fact that they put through the deposit from a nonexistent account is their mistake, not my floating a check.

In your world perhaps.  In the real world you are on the hook with your bank for money you withdraw against a bad check.  Ultimately, the client that wrote you the bad check is responsible for the original amount, plus your overdraft fees.

Not what you wanted to hear, but those are the rules.

You just admitted that you wrote checks for items and/or services on a check that hadn't cleared.

This is against the law.