The voice is always in a state of becoming. It changes as our bodies change, as our emotions change, and as our environment changes. How can there be a perfect standard when we are never finished becoming-growing-developing? There can be a high standard, developed from wonderful examples, but even our heroes were always changing in some way or another. Recordings can lead us to think that perfection was achieved, but they are only a semblance of reality if they are unedited. With editing and processing they are a new hybrid creation, based on somebody’s singing.
Prepare as well as you can, then let go when it’s time to perform. If you try to control everything in performance, you won’t do much that is interesting or inspiring. If you are more concerned with being right than being inspiring, you probably should not sing.