This document on ni.com details all the ways that LabVIEW classes can preserve data values that typedefs of clusters cannot. It goes into detail about what type of data edits can be preserved, what the effects of renaming a class are on the class, its descendant classes and its caller classes (those that use the renamed class as a data member).

http://zone.ni.com/devzone/cda/tut/p/id/6316

All of this preservation of data and the automatic mutation of flattened data from one version of the class to the next is possible because of the format of LabVIEW classes when flattened to a string. That format is documented in another LAVA thread.