Magdalen could be stretched to Maddie, I think, but not Mathilda. It's just too close to Mattie so It'd cause no end of confusion, a bit like nning Timothy, Tom IYSWIM. Prone to miss-hearing as the known nn.
I don't think there really needs to be any logic or sense to nn's though, wouldn't batt an eyelid at Puffin for a Rosalie.