Please note, Cell.StringValueWithoutFormat was originally provided for some special purpose according to some users’ requirements. It is not designed as "returning the string expression stored in the XML of the template file”. Instead, this property just gives the simple string representation of the internal object in our data object model. And, this property is not only used for those cells loaded from template files of ooxml format. For other file formats, there is no such kind of XML and then no such kind of string representation in the XML. Even for those string representation values, such as in ooxml, csv, html…etc., we don’t keep one copy of the representation in our model, so it is not always feasible to get the original string representation for a cell.
For your requirement, we don’t think this property is suitable as this property is not designed for such kind of requirements. As we have said, you have to check cell’s type and then build the proper string representation by yourself according to your requirements.
Thanks for your understanding!