Significance of sharing an entangled state in Superdense Coding

Superdense coding is a protocol used to transmit two classical bits of information from one party to the other by using only a single qubit and no classical communication between them. It is a corollary of Holevo's theorem that 1 qubit can not hold more than 1 bit of information. A communication protocol which demonstrates the transmission of 1 classical bit from (say) Alice to Bob via a quantum channel would be that Alice prepares a qubit in either of the states |0> or |1> and transmits it to Bob. Bob then measures it in the computational basis to recover tha classical bit. This protocol only conveys 1 classical bit while transmitting 1 quantum bit (so no entanglement is involved). However, if the two parties already have a shared nonlocal resource (the 1 ebit), then it is possible to transmit 2 classical bits via superdense coding, at the cost of consuming 1 ebit resource. (The shared classical information would be private as well due to maximum entanglement in shared qubits). Once they have a shared ebit, Alice only needs to transmit her (single) qubit to transmit 2 classical bits (apart from applying local operations). The distinguishability of the Bell states upon a measurement in the Bell basis by Bob is where the entanglement is being used to achieve this. The increase in the number of bits conveyed per number of qubits transmitted is increased, but only at the cost of Alice and Bob having shared an entangled resource in the past.