Error Code 19 denotes a situation where the engine could match the address in the Zip4 data, but was unable to DPV verify, so the result is no match. In previous versions, the returns were ambiguous, as the error code would be zero (or blank if using desktop) but the DPV result would indicate a match failure. Error Code 19 is a result of removing the ambiguity.
If you do not update your mDesktop/mSQL software, this error code 19 will be returned automatically when you update the data, if you do update your software though we've added a new option which will by default keep the return codes the same as the old version.
If you do updates based off the addrscore (mSQL), or errorcode (mDesktop), then you will either need to update so as to not impact your process, or adjust your process if you believe this change will impact you. On most clients data this normally would impact is less than 1% of the data.