I have decades of experience working with Vinyl and one thing I will suggest if you encounter stubborn adhesive that leaves residue is how to minimize the likelihood of residue being left behind.
If you remove vinyl by peeling it back you leave a very small area exposed which allows the adhesive to detach itself from he media and remain on the surface you are trying to take it off of.
What you want to do is carefully lift a corner and slightly stretch it outward as you lift it off SLOWLY. Think 3M adhesive Strips and how stretching them is essential to clean removal without leaving residue.
Believe me, I've stripped about 100 vehicles with vinyl baked and stuck on by the Florida sun and excessive heat & humidity over a 3+ year period and this is the cleanest way to remove vinyl. When lesser quality material is used, trust me, you will know it and you will need Rapid Remover which is one of the most expensive liquids you will ever buy at $55 per gallon. LOL
Paul,
My advice to you is to ensure your supplier is using either 3M or Avery Vinyl because they have the best adhesives in the market since forever.
And yes, I just threw that Illustration together for you guys.