Valve stem seals wipe off excess oil from the oil squirted out the push rod tubes to lubricate the rocker ball and to cool the valve springs. There are a lot of factors determine how much of the oil actually gets on the valve stem. Don't think a staic test will work. A flash light and an inspection mirror would allow you yo look inside the valve springs to see the seal.
I use white nylon with a stainless spring Perfect Circle valve stem seals that require machining the top of the valve guide. I bought a special cutter years ago and machine the valve guides in my drill press, then press them on by hand. The factory used a rubber umbrella for a seal that may not fit well inside high performance springs (double wound or conical). If the rubber seals don't fit, then a lazy builder would leave them off entirely, rather than address the problem.
Either way you can see the seals or the lack of them if you look.