Yep, dyes penetrate into the wood, so putting them on top of the shellac (it is done at times) doesn't get you the same coloring. Then putting the varnish on is the normal order. Now, if the dyes are alcohol based, putting shellac on them is a really bad idea (it redissolves the dyes and makes a mess. Also, a lot of folks go straight over the dyes with the varnish. I prefer to use the shellac easy enough to do and still gives a good look. But I suspect it's use in sealing the dye is more useful when the topcoat is a waterborne. Putting that on a water based dye is akin to putting shellac on an alcohol based dye.
Zinsser Seal Coat is their only dewaxed product. That said, the adhesion problems usually occur with urethane resins in the products, and some waterbornes. Waterbornes are actually acrylic resin finishes, despite what the name/label says. Some of the manufacturers add a small amount of urethane resin so they can include that magic word on the label. Even so, the can be adhesion problems with waterbornes but it's probably worth taking the chance.
Not exactly, they just add a small amount of the urethane resin, no oil based materials. All waterbornes, regardless of whether they are titled "lacquer" or "polyurethane" or "Grandma's magic finish" laughing are basically the same, an acrylic coalescing finish. Somehow, we woodworker's seem to have collectively accepted anything labeled "polyurethane" as the finish to end all finishes. To capitalize on that, manufacturers started the practice of added a small amount of urethane resin to the mix and labeling it to maximize sales and misuse. Since I'm not in the marketing discussions these guys have, it's all just my opinion.
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