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Notarium question

Some pterosaurs have an obvious notarium.

Others obviously have no notarium.

And then there are others.... somewhere in between... it seems to start with a anteroproximal lengthening of the vertebral spines... in the next taxon they're touching one another... in the taxon thereafter some actually fuse in certain portions, but not all the way...

And I haven't even mentioned the scapulae yet. In some they are nearly parallel to the vertebral spines, so, no factor. In others they are transversely opposed and obviously somehow joined to the vertebral spines, but in some cases the spines remain unfused. No notarium.

Question is, when is it valid to call the structure a notarium? What Rubicon must be crossed?

 Is there such a thing as a pre-notarium? or proto-notarium?

And if such a structure evolved more than once, should we differentiate these? Should we score them differently?

While others sleep comfortably, I'm tossing and turning      : - )

David Peters