Yup, you can dink around with stuff that's 5-10k and keep most or all of it in your head and scroll rapidly back to any spots you missed but you get up over that amount and unless you've got some kind of photographic memory... well I certainly can't keep up with it all. Its easy to remember the story. But the name of some guy you mentioned 60k words ago? Not gonna happen unless he's a primary secondary character.
I also like to save these things in as many places as I can. Cause you never know when your computer is going to crap out on you. I've lost three lap tops over here in the philippines. Thank god for flash drives and curse me for not updating them as often as I should have.
The Deposed King
I started using Scrivener and it has worked wonders organizing my writing. I second TDK's advice in following the words of the late great George Carlin, "Write everything down.". In scrivener I make separate text files for each bit of pre-writing stuff. I have a text file for each individual character, each major piece of world-building and a file for the outline material. When I write scenes I'll have it splitscreened with one window open to where the chapter is being written and one open to either the character write-up, the outline or more commonly a reference photo of some kind to keep the tone and imagery I'm trying to evoke in mind.
I also use a flashdrive with my work Laptop but I recommend backing up your stuff a lot. Don't end up like me and lose a hard drive halfway through a quarter...
Meanwhile...
In my writing life recently I did something cool:
I was spinning my wheels too much on a major project in favor of the beginnings of a new project for a 200,000 word novel. I don't have the time, energy or brainpower to work on the new novel right now because of more important projects so I had to put it to the side.
But, being unable to get it out of my head and with my previous writing projects falling apart because I hadn't planned enough I did something I had never done before. I thought a Project Plan all the way through.
To explain, I am going to school for Project Management. A big part of Project Management is thinking the steps of a project all the way through to completion and beyond. I had never approached creative work this way before taking the classes so the other day I decided to approach novel writing with a little Project Management.
I wrote up Objectives, a Mission Statement and did a Work-Breakdown Structure for the lifespan of a Novel Project from pre-writing to final draft.
I also broke the work down in Microsoft Project into hours and sometimes minutes. I had to because I usually don't have a schedule and as a result I will get distracted and never get anything done. Now I have a schedule
I ended up with a Microsoft Project Template I will use for other projects that came out to 56.7 Days of work + however long it takes to get to 200,000 words in days.
It humbled me to realize that if I started on the project now full-time I wouldn't be done with it until Christmas...