That’s what I used to think as well. The tank referenced to in this thread got its “+” rating back on this test. I inquired. Was told they do a bit more testing to see if it can meet that standard; it did. Hence the “+” after it having not had it for ~ 15 years.
did not know that, i always thought once it was gone that was it, as i have never seen it come back
i would personally rather have the 10 year star over the + myself, dont often see a 10% over filled bottle, and never if your getting trans filled bottles
now if they could turn a 5 year bottle into a 10 year bottle i would pay double the hydro test fee just to save the hassle of having to bring it back in 5 years!