I wonder, if there is no evidence of inks, dyes, etc. accompanying these marks in velum, could this have been a medium under the directly marked medium? So two

I wonder, if there is no evidence of inks, dyes, etc. accompanying these marks in velum, could this have been a medium under the directly marked medium? So two "sheets" one on top of the other where this sample was on the bottom of and another that was being marked was on top and we're left with these enigmatic doodles and scratches?