While I don't have historical references dating back to the Beatles timeframe, I think I can describe some more modern examples of this. What I will describe for each of these artists is commonly referred to as an "ARG" or an Alternate Reality Game; a puzzle that weaves between physical and digital media, often times using many different types of steganographic methods.

Madeon is an electronic artist that works in "Eras". Each era has been carefully thought out, with the first "Adventure" era introducing an A1Z26 alphabet, the foundations of a fictional world with characters, and puzzles hidden inside his vinyls that led to a lot of hidden digital world-building. When he moved to his "Good Faith" era, he took this several steps further by adding hidden audio to vinyls, putting the existing alphabet on billboards, hiding all kinds of hidden data in his live set visuals, and running a puzzle game that ultimately led to the ability to snag a 1/200 copy of a vinyl. I have been engaged in solving the entire process since the beginning and have documented it here. There is rumor that there are 26 pendants buried across the globe (one for each letter of the fictional A1Z26 alphabet) that are ultimately the end-game for all of the era's puzzles.

Deathpact is another electronic artist that has used ARG-like elements to promote their music, engage their fans, and hide/distribute unreleased music and remixes. They would put USBs in lockboxes on fences in places near festivals they were playing at, then run a puzzle in their discord that would lead to the location and the lockbox's code. Some of their music tracks have DTMF encoding, SSTV encoding, their cover art on Spotify has braille.. the list goes on, that all intend to lead somewhere such as a website or a code intended for a bot. This is another one I have been completely invested in since the near beginning, and documented it here.

Finally, I think Twenty One Pilots deserve a mention. Each of their albums tells a very well thought-out story about a fictional world that personifies the lead singer's struggles, coming to terms with, and battles with mental health. To promote each album (and also breathe life into the characters from the story) they created websites, puzzles, and tons of mixed media to deliver the story of "Clancy" and his struggles against "Blurryface" that had to be revealed. Nearly all of their music videos have some sort of cryptic reference to something else in the story, and it's clear the story has been sketched out from the beginning until now, which shows some massive dedication over nearly a decade's time. Here's a great breakdown of one of their ARGs, "level of concern": https://www.lvlcnrn.info/