Quinten,
You are way over complicating this now that we under stand your question. Had you stated your actual use case we could have more easily helped you.
Just make a summary field on the relationship to count the # of document of a particular type. say Type = Liability.
Then make a formula field on the parent Contracts record called [Contract Documents Loaded for Liability]
IF([# of contract documents for Liability] > 0, true)