Your examples are a problem of semantics. Truth is a property of propositions. So when you make propositions about truth, they get wonky. The same thing happens when you make propositions about existence. (in the latter case, because existence is a quantifier, not a predicate)
In mathematical logic perhaps “existence” is said to be a
quantifier acting on a
predicate
Thus,
∃xPx is read as: "There is an object having property
P ".
The
existence of that particular object is a fact that is not ascertained through the mathematical or logical statement. It’s existence
requires an empirical verification or A PROOF.
Existence, in the case of contingent entities is not part of the “concept”
P itself, but existence may logically be an aspect of necessary being(s). Aquinas proposed just that to be the case.
There is a great deal of debate over necessarily existent entities. Various forms of the ontological argument actually propose that God as Necessary Being either exists necessarily or logically cannot exist. This would be precisely because
a necessarily existing being that only possibly exists would be a self-contradictory proposition. Ergo, God
either exists of necessity or cannot possibly exist.
If there is no logical impediment to the existence of God then the proof would stand as a PROOF, i.e., answering the mathematical requirement that IF the
existence of a particular object is a fact that is not ascertained through the mathematical or logical statement alone, establishing it’s existence would require an additional empirical verification or A PROOF that a necessary existent must exist as a logical necessity.
In fact, if God’s existence can be demonstrated using an empirical or cosmological argument (empirical verification) and conversely by the ontological argument as logical proof, then what we have is the same kind of symmetrical demonstration as Newton’s inverse-square force of attraction that conforms to the observed orbit of any of the planets around the Sun as a conic section and the converse that if its orbit is a conic section the planet must be attracted to the central source by an inverse square
law (Cf. David Berlinski,
Truth Really Matters)