yeah i do that. even when i remember the instrumental i forget exactly how the flow went. like sometimes i wont be in the pocket but i'll write with a flow that's slightly behind the beat and stuff. i dont really know a better way to explain it. but i was seeing if anyone had tips i could use
Well another thing I should point out is that flow is also sorta dependent on how you vibe with the song playing in the background. You know? Like you'll hear the instrumental and you'll just start mumbling with a certain flow and such, and then you start writing like that.
It's hard to really capture flow with your writing, because flow is more about HOW you say something, and less about what you say. You can slant rhymes or elongate or shorten pronunciation of certain words to fit them into your flow (How well you do it is up to you).
Your situation is a first for me really. You usually get a certain vibe from a particular song (Talking about the rhythm of the beat mostly, that's the backbone) which in turn affects your flow. So one would think that hearing the same song everytime would give you the same vibe, and hence you'll want to use the same flow.
What I can suggest is maybe you can come up with your own notation for specifying how you say those words in relation to the beat (flow). I think something like that exist, the coli MCs that are pros can elaborate on this.
I'm not an MC btw, just a fan of the artform :D.