I think that when the sharpening part is too thin, the blades need to be replaced... the sharpening part being the bottom of the blade, about 3-4 mm thick when the blades are new (I think... I read this somewhere). Also with time the rocker tends to even out so maybe make sure it's still good, I think the back end of the blade is supposed to be 1-2- inches about the surface when you place you blade on, say, a table. I can't be sure of this, though, because I read this article a while ago, but if you go to usfigureskating.org and into the SKATING magazine section, you can search Mr. Blade's answers over the years and he has written about blades at some point. Other than that I have no idea... sorry.
Kypma