Starting from Brhthari's vAkyapadiya, Sabda and vAk have the same meaning as in other texts like Rg Veda, Brhadharanyaka Upanishad, Mandukya Upanishad and saMkhya kArika, irrespective of their timelines, geographies and philosophies that were 'dug'out of them.
Sabda are 'oscillations'. vAk is the four-fold expression. It is the four-fold expression of Human speech. It is the four-fold expression of Universe by Atman. Thus vAk is the design pattern for the four-fold expression of Human or Atman.
Seven parts and Nineteen faces of Mandukya Upanishad
The seven parts and nineteen faces of Mandukya Upanishad are not specific to a particular state though they are talked about in the antaH-prajna and bAhis prajnA alone. It is because these two are are the external part of expressions of Atman or Human being.
The ekibhuta prajnA is the state in which there is only one bhuta, one manifestation and that manifestation is prakrti alone. Mandukya Upanishad maps it to deep sleep state. In terms of Universe it is the state in which there was only empty space or vacuum which had just energy oscillations (prakrti) and there was nothing else. This was the state during cosmic inflation epoch.
These nineteen faces of Mandukya Upanishad including the five tanmAtras are the 24 principles that saMkhya philosophy is all about.
Aham-kAra - That differentiates
Aham-kAra is that makes the 'Aham' the 'Self'. It is the one that 'differentiates' or 'diverges' or 'divides' between matter forms and gives them the identity.
From the state of ekibhuta prajna, the prakrti, the energy of background quantum oscillations in vacuum, various force-feilds or Rudras manifest or get divided and diverged. From a Unified Electro-weak-Strong force, strong force separates, then electromagnetic and weak force separates. From a Unified Higgs field that does not interact with matter, higgs field that interact with matter manifest.
All these are 'Aham-kAra' or creating individual identities.
Thus Aham-kAra, that differentiates and gives different identities arises from prakrti (background quantum oscillations) but exists at all times in the Universe.
In Classical thermodynamics it could be the 'internal' energy of an object/matter form or zero-point energy of a particle manifestation, that differentiates objects and gives them specific identities.
In Quantum world, it is the Rudras the force-fields that continuously divide from being a single unified force into multiple manifestations of force-fields.
Fourth verse of Mandukya Upanishad
In Universe's expression, the second part is like a dreamy state, in the sense, it is a probabilistic state of existence unlike the 'sthula' which is deterministic.
Both Classical and Quantum state are matter forms. Classical is deterministic/gross/sthula and Quantum is probabilistic/subtle/taijasa.
The seven parts and 19 faces are characteristic of matter forms irrespective of being probabilistic or deterministic.
Fifth verse of Mandukya Upanishad
In Universe's terms it is the state no excitations (kAma) exist. It is the state in which Prakrti, the energy of background quantum oscillations of vacuum alone exists. There are not even quantum force-fields. This was the state of Universe before Quantum force-fields manifested. This was the state of Universe during Cosmic Inflation epoch.
Ananda is not just bliss or happiness. Brhadharanyaka Upanishad says what is Ananda. It is the ability/potential to reproduce. When Universe is in the state of ekibhuta, where only prakrti or Quantum background oscillations only exist, it has the maximum ability/potential to produce. That is Ananda.
Sixth verse of Mandukya Upanishad
In Universe's expression this is the 'Virtual' particles manifestation that exist within every particle manifestation of Universe from baryons, mesons, nucleus virtually, that joins them, that creates everything and hence knows everything in the Universe. It is the 'Manas'.
Summary of Mandukya Upanishad
Om is the akSara of everything, unto it, is explanation for matter present, future etc (and past). All the matter past present and future are made by Om and hence the Universe is om-kAra, made by OM. OmkAra means 'made by Om'. This is beyond time, time as we see in tri-kAla (past, present, future).
Om is the cosmic sound produced by baryonic acoustic oscillations. It is the first acoustic expression or sound and hence called praNava. Since Om is the first acoustic expression produced in the Universe as baryonic acoustic oscillatitons, all our expressions start with Om.
More important, this Om is what created the gravitational seed of galaxies, from which grew the stars, planet and us biological beings. Hence this Om, the first cosmic sound, the pra-Nava, the baryonic acoustic oscillation is the cause of all matter and beings of Universe.
All of these (Universe) are brahman (evolution). This Atma is brahman/evolution. This evolving/brahman, expression of Atma is of four parts.
The first part is Vaisva-nara. It means the Universal matter. Nara is the mortal matter. Visva is universe. Vaisva-Nara are those Universal mortal matter forms. It is like 'waking up' state of consciousness. Hence it is called 'bAhis prajna'.
Vaisvanara is the 'Classical' matter that we observe. They are the 'sthula' or 'gross' or more precisely 'deterministic' matter form.
The second part is Taijasa. Taijasa is like a dreamy state, in the sense, it is a probabilistic state of existence unlike the 'sthula' which is deterministic. It is called 'antaH-prajna' or the prajna inside.
Both Classical (Waking up) and Quantum state (dreamy) are matter forms. Classical is deterministic/gross/sthula and Quantum is probabilistic/subtle/taijasa.
The third part is Ananda. Ananda is a state where there is no excitation (kAma), not even quantum fields (dreams). This is the state which has the maximum potential to produce matter (Ananda). This is the state in which Universe exists in just one form. It is the state of Universe in Cosmic Inflation epoch, where there was only energy in quantum oscillations of vacuum, which is called prakrti. Hence it is called 'eki-bhuta prajna'.
The fourth part is not just the source of everything. It is what exists inside of everything, joins them and makes them to function homogeneously. Since it is 'inside' and controls, it is called 'Easwara' of everything.
The design pattern of vAk
vAkyapadiya in terms of ‘expression’
Rgveda in terms of Universe
Upanishad in terms of biological being
Upanishad in terms of consciousness
saMkhya kArika in terms of Instruments of Atman, the karaNas
Background quantum oscillations of vacuum
Aham-kAra that makes the ‘aham’ or ‘self’
Probabilistic Quantum force-fields
Caksu (Point/Buddhi), Zrotram (Process/Karma)
Ten Indriyas as bAhya karaNas
Deterministic Classical particles