I'll assume you've seen the film. Spoilers ahead.
So: I got to the 'I know who I am!' scene. Then Cypher says to Johnny: 'for twelve years you've been living on borrowed time...'.
I thought 'hmm'.
Because, typically, the faustian bargain lasts 24 years. It was as if the film was saying 'look for the other half'.
I did, and found something interesting. There seems to be two bargains. One made but not complete; one complete but not made:
1-As we are told, Johnny made a bargain with the devil before the war. Let's say a 1939-1963 bargain.
2-But the devil returned to collect Johnny's soul in 1955, so the bargain would have been made in 1931. But Johnny made no bargain back then!
The explanation seems to be obvious: Johnny tried to duck out of the 1939-63 deal, but the devil had foreseen that possibility and switched to the 1931-55 bargain.
So Cypher was already there in 1931, when Johnny was a 13 year old boy. Maybe laying some kind of subconscuous backdoor through which he could guide Johnny's hand if he tried to trick him. And that's what we actually have in the film.
Now in the novel, Johnny's secret love Evangeline Proudfoot is ten or more years older than he. But in the film, and as we can see (the date on her gravestone), she had been born in 1918, just like Johnny.
Alan Parker changed that. Why? Remember what Ethan Krusemark says to Johnny in the 'it's a crock of shit!' scene: [Johnny] needed a victim, someone his own age...to steal their soul
So did Alan Parker, I guess. Johnny and Evangeline had to be of the same age for Cypher to lay a hook on his 'favorite' Johnny Favorite.
Maybe that's how Cypher laid the backdoor, through Evangeline, who was a voodoo priestess at that age, and therefore connected to the demonic, just as her daughter would be.
And that's what we see in those dreams. The woman in black (whose face is DeNiro's, as we can see at the end).
The song 'girl of my dreams'. Maybe Johnny had already seen Evangeline in her boyhood dreams, before actually meeting her.
According to Epiphany, Johnny 'stole her mother's heart', a pretty banal line in itself, but maybe not in this film. Nothing is given without something being given away and vice versa. So maybe Johnny lost or compromised a piece of his soul back then - before the 1939 bargain. And yet, and as Cypher says, it was killing Angel in 1942 that doomed him.
'He needed a victim, someone his own age'. Johnny had been born on Feb.14 1918. Evangeline had been born in 1918, but what about her birthdate?
We don't know...but Parker himself had been born on Feb.14.
13 year old Johnny and Evangeline. Precocity seems to be a thing in this film. Margaret Krusemark, who was into tarot card before she could read. Epiphany, a voodoo priestess since age 12/13. The names Johnny (not John, as in Johannes Faustus) and Harry (not Harold). Both are called 'boy' in the film.
So this idea more or less fits with this theme too, and obliquely so with films like The Exorcist and the 12 year old Regan girl. It was about sexual awakening in a way.