Hi there, hopefully you'll get some Spangles soon. Having the Pied in there will be reducing the chances of getting the nice clear Spangle markings as you noticed on the Spangle Pieds you've got. It could be that your combination pied chick is Spangle for instance.
The pied head patch can indicate that they are split for Recessive Pied, or in some uncommon cases can be Dominant Pieds without much pied marking. If you have a combination pied chick it is very likely that they are split for Recessive Pied though.
Pics would be great!