Why can't I delete certain Note Types in Picklist Maintenance?

Note Type	What does it do?	Related Dashboards/Reports

Note Type	What does it do?	Related Dashboards/Reports
Contacts	Used for Notes added to Contacts
Defendant Insurance	Adds note to Defendant Insurance screen
Email	Adds note to Emails screen
Expert	Adds note to Experts screen
File Review	Notes date of most recent File Review	Attorney File Review Overdue Dashboard Attorney Performance Dashboard Attorney Performance Report Overdue Report Staff Performance Dashboard Staff Performance Report
Investigations	Adds note to Investigations screen
Phone Call	This note type is used to create a note when click to dial is used (you do not have click to dial set up, but you can still use this note type for phone calls manually)
Plaintiff - Contacted	Notes date of most recent Client Contact	Attorney Performance Dashboard Attorney Performance Report Client Contact Overdue Dashboard Overdue Report Staff Performance Dashboard Staff Performance Report
Plaintiff Insurance	Adds note to Plaintiff Insurance screen
Police Report	Adds note to Investigations screen
Supervisor File Review	Notes date of most recent Supervisor File Review	Staff Performance Dashboard Supervisor File Review Overdue Dashboard
Task	Used to show completed tasks on Notes screen, and for notes about completed tasks.
Witness	Adds note to Investigations screen

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