If you guys are serious about stopping the patina at a certain stage, or maybe even at fresh virgin vachetta you should contact a reputable leatherworker. I know that they can treat the leather with their special chemicals to fix it at a certain point. It may not be possible with some models, if the vachetta is positioned in a way thats too hard to treat without affecting the other material. LV vachetta is natural untreated leather so essentially they are just adding the treatment.
My mom took her old noe in to a leather repair shop for reconditioning. The patina was REALLY dirty and waterstained, what they did was some sort of steam cleaning and then used solvents. They put this protective wrap around the vachetta to cover the canvas. The patina turned out a deep beautiful shade that was all even (no more waterspots!). Then they sealed it with some type of protectant, the leather guy said it would never change color and no more waterstains would occur.
My mom took her old noe in to a leather repair shop for reconditioning. The patina was REALLY dirty and waterstained, what they did was some sort of steam cleaning and then used solvents. They put this protective wrap around the vachetta to cover the canvas. The patina turned out a deep beautiful shade that was all even (no more waterspots!). Then they sealed it with some type of protectant, the leather guy said it would never change color and no more waterstains would occur.