Then why not test for the presence of a group code 6?
These could be different things. Do you want the hidden and center, the bylayer, or both? If it bylayer you want see above. If it the others, test for the line types in the group code.
It was answered. Test for a group code 6. If none exits, it's bylayer, in which case you'd have to check the layer's linetype setting.
Can you search the layer definitions for layers with "Hidden" and "Centre" linetypes?
If you can, copy each such layer name to variable then search for elements on that/those layer(s).
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