Question what do you all mean by AFAIK. Im not as young as you guys. I was born in the 70's
Hitler was still running the The Turd Reich, Roosevelt the USA, and Hiroshima and Nagasaki were still "going concerns" when I was born.
Coms links were SLOW, character-count was precious. Private company, government organization, or major telegraph carriers alike all had "code books" to get more for their money in less time. The first "girdle 'round the Earth" predecessor to the internet, completed 1898, was only FOUR WORDS PER MINUTE capable, and time-of-day alternate SIMPLEX (one-way at a time, then change-over and run traffic the other way) at that.
The British Government had absolute priority over all comers on that "net", a message that traversed in two minutes might have waited two WEEKS in the queue before rising to the top of the pile, then require another two DAYS at the receiving end to rise up the pile being decoded and finally being dispatched for delivery by bicycle courier.
As link speed grew, need for the use of it had grown as fast or faster, so all this wasn't THAT much better by the onset of WWII, or Pearl Harbour would not have been a "sneak attack".
I first learned telegraph codes such as "NNN" for message eNNNds. Amateur Radio had a set of their own, too "73" being a common way to end an amicable session.
You can look most of those up, same as those used on the 'net, such as IIRC, AFAIK, FWIW, and far more used nowadays on handhelds by the sexting ear-bud generation.
Oh.. one bit of irony.. modern packetized messaging has so VERY damned-much error-correction and recovery, security encapsulation, and outright GARBAGE attached as protocol "headers" and logging evidence that it NOW takes 10 to 20 times as much bandwidth to move the b****y "overhead" as it does the actual content of a message.
Send yourself a test email message with 8 bytes. "TEST" as subject. "TEST" as the only text.
Typical size will be 5 to 8 KILOBYTES at the receiving end.
Headers, mostly.
Progress? Go figure!
NNN