What is the best way to store data for exceptional cases among nested objects in arrays in JSON?

I have a JSON object with a huge array of nested objects. Let us assume it consists of records of license plates for vehicles. It would contain necessary fields like licenseID, issuingState, dateOfIssue, driverID etc.

What I am having problem with is how I should store data that is only used for exceptional cases, like a field for representing if the license plate is for foreign embassies (isEmbassyOwned) or if it is owned by a government entity (isGovernmentOwned) or if it is a learner license (isLearner) etc alongside fields with data types other than Boolean which would be empty or 0 and likewise when there is no information on that field. Let it be known that these exceptional scenarios would occur in less than 10% of total object instances.

I am facing confusion as to what format would be best for storing such type of data keeping balance between minimizing storage consumption and being human readable. Should I declare the fields for all objects regardless or only include them when they are not empty? Should I store them in a dedicated array instead, or maybe just introduce some code value to be used by a switch case operator in the interpreter? Or is there some other implementation I am not aware of?