Date for late refunds: process or check date?

I've heard that we are supposed to go by the check date to determine if a refund is "late" or not.  For example, if a refund is processed March 15, but the check date is March 16, then it's considered late and the penalties apply.

Do the IRS folks really look at the check register?  Wouldn't they use a transaction report that shows the distribution was done on 3/15?  has anyone ever been dinged on that?

What if it's an ACH that doesn't happen for two or three days?  There is no check register to, pardon the pun, check.

For purposes such as whether a corrective distribution was made by March 15 or April 15 (or such a date as adjusted under a holidays rule), I’ve heard some providers reason that a distribution is made on the day the instruction is processed such that mutual fund shares are redeemed, or collective trust fund units are withdrawn, as of that day.

Do BenefitsLink mavens concur?

If it causes the participant to not have those monies in their account as of that day then yes.