General CMOS circuit
in any circuit can there be a lower voltage with respect to the negative terminal of the source

Totally different question. The answer to that is obviously &quot;yes&quot;; you know that transformers exist, for example.

In any circuit built from MOSFETS can there be a lower voltage with respect to the negative terminal of the source

Well, I assume that if you understand CMOS, that you also have basics of linear networks.
So you can answer that yourself, negatively, if you model all your transistor source-drain connections as resistive elements.
If you introduce parasitic inductances or capacitances that you use to build inverting power supplies, yes, you can get lower voltages and your original claim breaks down.