Matter Plans are assigned automatically to newly created (or imported) Matter records when the Case Type field on a Matter Plan record matches the value in the Case Type lookup on the Matter.
To avoid auto-assigning them:
Clear the Case Type values on the Matter Plans before importing Matters to which you do not want to assign Matter Plans. Do this on the list view of Matter Plans or on each individual Matter Plan.
Make sure to re-enter those Case Type values before importing Matters to which you do want to assign Matter Plans. These values should also be present prior to User Acceptance Testing and go-live.
One Matter Plan per Case Type
Only one Matter Plan in each org should be assigned a given Case Type (e.g., "Automobile Accident"). Treat those values as unique. Multiple Matter Plans may still be relevant to a given Case Type, but only one will be auto-assigned — the others may be reached via Matter Stage Switches.
Some firms may prefer to import all Matters without Matter Plans; others will prefer to import open/active Matters with Matter Plans assigned and closed Matters without them. The implementation partner project manager should discuss this preference with the project lead on the firm side.
Importing Matters without Matter Plans