I should be very interested in the answer to what accuracy film capacitors (or any other capacitors..) are produced in the first place... Can it be that they just produce ANYTHING around 10 nF and then select whether its closer to 5nF or 20nF, and leave it at the (typical!) 20% error?
I would think - as said - that a PRESELECTION for 1% seems wasteful.. Who would take all those values to be kept in store in the meantime?? So may be order triggered (!) selection will take place...