When does Human Factors stop being the 6Ms and start being actual human error?

Tricky situation here - we are talking data management. Data management with expected high accuracy...

If you have done the 6Ms but they really do not explain the error rate, what percentage error rate would you consider significant for manual data entry?

I have previously worked to 0.5% for transfusion error, and 1% for other areas.

I am in a new role which includes quality managing a highly manually entered database - I have risk assessed it and the risk assessent has allowed me to get funding for a replacement, but this could be many months down the line before it is implemented. As part of the risk assessement, and annual audit, I have audited the data and am now looking at tolerances, but don't want to be unacceptably stringent. But on the other hand being lenient can't happen either due to the required accuracy of the data.