I tried with 3 images with following commands, it is working fine:
- fdt2.exe -d wpspk -mi -f WP76xx_Release16.1_GENERIC.spk WP76xx_Release16.1_TMO.spk WP76xx_Release16.1_VERIZON.spk
- fdt2.exe -mi -f WP76xx_Release16.1_TMO.spk WP76xx_Release16.1_VERIZON.spk