How to ensure a journey builder entry/filter criteria only validates when the field was just changed to that value, to avoid duplicate emails being sent

I', very new at marketing cloud and I just finished a journey builder, that both checks the status value and isMarketing__c value of cases 

I have a normal flow that after a bunch of important validations, sets the custom field to true if it needs to be tackled by marketing cloud, and my journey which I have selected both as created and updates cause I need to process cases when status is "New" or "Closed" and custom field is true 

But I just found out searching for information before activating it, that apparently journey builder will launch every single time a case has another field updates if it is already New/Closed and True, cause it doesn't validate if the 2 fields have just changed to said values. 

My question is, is this true? and if yes, how can I tackle this issue (I can't just deny re-entry cause the contact should be able to create multiple cases and receive email for each of them), also will the fact the custom field is update to true in a flow affect how journey "receives" the case?     I haven't seen anywhere the choice of "only when fields change to meet the criteria" or something similar