Called the NVC last week with my questions, and am passing along their response in case anyone is or will be in a similar situation with similar questions, and also to encourage anyone who already successfully navigated our situation to share their own experiences: The NVC customer service representative told me that, despite the 2D barcode that alters as it records the information input, the I-864 was not designed for electronic completion, so completion by hand is recommended.  She veri