One way to protect against false positives in a pattern or dictionary phrase is to exclude certain values that falsely match it. When creating the classifier, define a Pattern to exclude that lists words or phrases that are exceptions to the rule (search for all Social Security numbers except these numbers that look like Social Security numbers but are not).

You can also add a List of strings to exclude listing words or phrases that, when found in combination with the pattern or phrase, affect whether or not the content is considered suspicious. These fields are available for both Regular Expression classifiers and dictionary classifiers.