I noticed the symbol thing on the very first Yummy we saw (the mantis one) and the Greeed, but I haven't noticed what others have mentioned about the Dopants and Gaia Memories
I don't see a point. It seems that the incomplete combos are just stepping stones towards the complete forms, it's just parts swapping, not creating new abilities with new combinations. Apart from TaToBa, I don't see how any form bar the complete has any significance.