Salesforce: Clone & Fields in Page Layout

Clone

• When you clone a record, by default, fields that are not in the page layout will not copy to the new record.
• If the record you’re cloning or a related record contains a field you don’t have access to, the field in the new record is blank.
• If the record you’re cloning contains a field you have read-only access to, the field in the new record is blank.
• If a related record contains a field you have read-only access to, the field value is copied into the new record.

Related List

When you create a child record from the parent Related List, even the parent field is not in the child page layout, the parent value will be populated.

Reference:

• Clone does not copy the field values for fields that are not on the page layout
• User see a Related List on a Parent object when they do not have visibility to the child object's lookup field