You can define the rules for the internal consistency of data by seeing how different pieces are related together. By deduction, you can gather enough samples to support the definition of a rule. If you are so brave and lucky to come up with the internal consistency of the data you have gathered, then you need to apply those rules to the whole data inventory. Without knowing the rules at the source of that data you can increase its quality by applying the deduction you can make.
Senior Experience Designer. 25 years designing, developing, writing, speaking, facilitating and teaching.