Doug's comment about weighing stays/blades is what I have been doing for quite a while. I haven't seen the amount of variation between "the same" stays that he recalls but they do vary. (I suspect the wear tolerance range of tubing dies and mandrels has gotten smaller since the 1970s when Doug and I started doing this stuff).

When I receive tubes from a supplier (not too often given my 1 frame a year production) I do a series of checks. For main frame tubes I mark the butt transition portions with a butt checker and I roll the tube on a flat surface to mark the tube's bowing high point. For stays and blades I weigh them, note this on them and pair them up based on weight. (IIRC blade or stay might vary by a few grams). I wrap some masking tape on the tubes with any data I've discovered then coat the tubes with LPS-3 for storage rust control. Andy (who now can't find his little electronic scale...)