To exclude false negatives when comparing obtained data, Document Reader SDK has a special parameter set by default not to perform comparison of text fields with low OCR probability.
You may change it in order to ignore recognition probability check and perform comparison of obtained data anyway. This parameter can be set in the RegulaReader.ini file.
By default it is located in C:\Users\<user>\AppData\Local\Regula\Document Reader SDK\ folder:
See section 5.4.33 of the Programmer's Guide for possible values of the LexAnalysisDepth parameter.