NEC ECC: What happens if a Project Manager assessment is underestimated?

If following implementation of a PM assessment of a CE, the PM realises the assessment has missed a fundamental aspect of cost, how can a correction be issued? Cl. 60.1(17) deals in corrections to assumptions the PM has made in connection with a CE. In this case no assumption was offered.

Under clause 60.1(8) if a Project Manager changes their previous decision this would be a compensation event. They can then assess a new CE for the element that they agree they have missed. However, this clause can only be used to increase the total of the Prices, never reduce. So if they have ever over estimated an implemented CE they can not reduce this, only ever increase IF they agree an element was missed in their assessment.

I have a doubt if PM assessment of a CE is one of the decision as defined in 60.1(8). If anyone can help to clarify.