[SalesForce] How to get previous value in formula field

You can achieve this without Apex by using Process Builder on DocuSign Status.

Filters: You would want to filter that the DocuSign Status corresponds to Sample Order as follows:

• Field - use your lookup as the field, but make sure you use the lookup (ends with __c) and not the relationship (has a right arrow).
• Operator - startsWith
• Type - Id
• Value - use the first three characters (key prefix) for any Sample Order Id. For example, if it were to Account you would use a filter value of 001.

Action: You can then set the field you want on Sample Order from the DocuSign Status.

• Action Type - Update Records
• Action Name - whatever you like
• Field Update - select the same lookup as in your filter, set type to reference, and find your field.

You can try apply the following logic in your formula. The example goes 3 levels deep but can be extended to 7 as in your example.

IF(len(Parent.Active_Contract_Number__c) >= 1, Parent.Active_Contract_Number__c,
if(len(Parent.Parent.Active_Contract_Number__c) >= 1,Parent.Parent.Active_Contract_Number__c,''))

Break down into steps:

1. Parent has Active Contract Number
2. Yes -> Take that value
3. No -> Try for the parent of my parent
4. Repeat 1 for parent of my parent.