"vinnana + without end" also narrows it down because;
Vinnana is a Sankhara but ("sankhara-vinnana" + "without and end") = impossible
Therefore ("Vinnana" + "without end") appears to mean that we are talking about about a ("Dhamma-Vinnana"+"without an end end") that would be possible. A reality that is not inconstant, not-impermanent.
Anicca implies Dukkha to the extent that inconstancy is unsatisfying and unreliable.
All formations are Inconstant
All formations are Unsatisfying
All formations are Not-Self
All formations are Dhamma
Not all Dhamma are formations
From this we can know that:
("Sankhara" + "not-Anicca" + "not-Dukkha" + Anatta) = impossible not possible
("Dhamma" + "not-Anicca" + "not-Dukkha" + Anatta) = possible not impossible
Therefore;
("Vinnana+without end") + ("Sankhara" + "not-Anicca" + "not-Dukkha" + Anatta") = impossible not possible
("Vinnana+without end") + ("Dhamma + "not-Anicca" + "not-Dukkha" + "Anatta") = possible not impossible
"Third Noble Truth" = ("Dhamma" + "not-Anicca" + "not-Dukkha" + "Anatta") = possible, not impossible
"Nibbana" = ("Dhamma + "not-Anicca" + "not-Dukkha" + "Anatta") = possible, not impossible
Couple important Sutta that i belive to explain why Nibbana can be referred to as "Vinnana Anidassanam"
Nibbana Sutta:
I have heard that on one occasion Ven. Sariputta was staying near Rajagaha in the Bamboo Grove, the Squirrels' Feeding Sanctuary. There he said to the monks, "This Unbinding is pleasant, friends. This Unbinding is pleasant."
When this was said, Ven. Udayin said to Ven. Sariputta, "But what is the pleasure here, my friend, where there is nothing felt?"
"Just that is the pleasure here, my friend: where there is nothing felt.
Mahavedalla Sutta:
"'Consciousness, consciousness': Thus is it said. To what extent, friend, is it said to be 'consciousness'?"
"'It cognizes, it cognizes': Thus, friend, it is said to be 'consciousness.' And what does it cognize? It cognizes 'pleasant.' It cognizes 'painful.' It cognizes 'neither painful nor pleasant.' 'It cognizes, it cognizes': Thus it is said to be 'consciousness.'"
Somewhat noteworthy is that both passages are attributed to Ven. Sariputta
DhP 203
Hunger is the highest illness. Conditioned things are the highest suffering.
Having known this as it is, Nirvana is the highest happiness.