The main Key Performance Indicators (KPIs) for the CMDB Health scorecard in ServiceNow include Correctness, Completeness, and Staleness. These KPIs are critical for assessing the overall health and quality of the CMDB. Correctness refers to the accuracy of the data in the CMDB, Completeness measures whether all required CI data is present, and Staleness indicates the freshness or timeliness of the CI data. Compliance and Duplicates, while important, are not considered main KPIs in the context of the CMDB Health scorecard.
References = ServiceNow CMDB documentation and CMDB Health Dashboard user guide, focusing on the key performance indicators for CMDB health.

One method for deleting specific CIs not discovered in 30 days is to use a scheduled job that runs a script to query the CMDB for CIs that have not been updated by Discovery for a certain period of time, and then delete them or mark them as retired. This method can help you keep your CMDB clean and accurate, and avoid having stale or obsolete CIs. You can configure the scheduled job to run at a specific frequency and time, and specify the criteria for selecting the CIs to delete.
References: Automated way to disable/retire CIs not updated for 45 days, ServiceNow CIS-Discovery Sample Questions

The $process.executableDir expression correctly calls the value of the executableDir variable from the tabular process variable. The process variable is a tabular variable that contains the output of the ps command, which lists the processes running on a CI. The executableDir variable is a column name that holds the directory path of the executable file for each process. To access the value of a column name from a tabular variable, you need to use the dot notation, such as $variable.columnName12.
References1: Pattern variables - Product Documentation: Tokyo - Now Support Portal2: Examples of EVAL scripts used in Discovery patterns - ServiceNow