I think I may have seen same video some time ago," Eller bros" ? maybe ? And the padding was most likely applied for creature comfort, not as a sealant ? then again, Maybe it was to be an overlay , the reason for gluing ?
You can make new holes for new seat cover stitching.
(or very carefully align old holes, hard to align real well) movement, stretching etc.
Once your pattern is as you desire, and tooling finished if any desired, I would apply any dying, staining, coloring, if wanted,
and then apply any jeweling, dots, decorative stitching/lacing etc. It can then be Stitched together making sure it fitted as you go.
I'm sure there are other ways of doing this, Others whom have more experience might do it completely different.. but this is what I think I would do if confronted with this myself.
Hope this helps in some way. Good luck ! Wild Bill46