If the technologies are similar, not much. However, different versions have been designed for different OS versions. Google basically took the software and recompiled it in each version of the JDE (except the latest). It may not be that much different from 4.7.1 to 4.5 (or whatever versions you have them), but it gets tricky when dealing with certain code that has been removed from newer versions or certain features that may or may not be fully backwards compatible.

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BCSA (4.1, 5.0) | BCSD (4.1, 5.0)

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