I didn't go over the score before we started rehearsals last week, as I was curious to see what I would remember. Last night, we worked on movements three and seven, running through them at speed. Some parts went straight from backbrain to mouth, with no conscious effort. Then, suddenly, a roadblock--a single measure where my brain shorted out. It was like I'd never seen it before. The measure was covered with pencil marks, I saw, but I didn't have time to focus on them. After we stopped, I was able to look at the marks, which showed me how the notes repeated (and didn't, in the trickiest spot). Once I saw how I'd marked it, the next time I sang it perfectly, as if my memory had been returned to me all of a piece; I could feel the memory in my voice. Or because I knew what the marks were, and this time a glance was enough to remind me what they meant.
I think this might be like spelling. There are those certain words which, no matter how many times I look them up and confirm their spelling, I still am not sure the next time I want to use them. This measure was clearly a problem for me the first time, as I'd marked it so carefully, so I had to learn it by rote repetition, not intuitively. Perhaps rote learning doesn't stick as well, deep down?
There were a couple of other little spots like that, but none so dramatic.