The MOST important measure of the effectiveness of risk management in project implementation is the percentage of projects:

Effective risk management aims to identify, assess, and mitigate risks throughout a project's lifecycle, preventing them from manifesting as high-impact problems in the production environment. A project going into production without high-risk issues demonstrates that the risk management processes successfully reduced residual risk to an acceptable level.

Regularly updating a risk register is a process control for risk management activities, not a direct measure of the ultimate outcome or effectiveness in preventing production issues.

Establishing Key Risk Indicators (KRIs) is a mechanism for monitoring risk, but it does not directly measure the overall success of risk management in preventing high-risk issues from reaching production.

Having an action plan for overdue issues indicates reactive risk management, addressing problems after they've occurred, rather than proactive prevention which is the goal of effective project risk management.