To Branadic......thank you for quoting me but you forgot to give credit where credit is due.
The reverse pi winding myth has been around a very long time, mainly a marketing thing. Actually, the real reason for multiple pi is for voltage ratings, the enamel coating on wire is quite thin by necessity, therefore using more than one pi reduces the voltage applied across each pi and reducing the likely hood of punch through of a pin hole in the enamel.
Bifilar winding is not commonly used in PWW resistors, it is not friendly to production, it is used in some special instances.
The unbalanced resistor from G.R. was much more likely a 24K unit, as one of the pi is practically empty leaving 12K, if it had been 18K, about half of the wire would have been left in the near empty pi as they would only have needed to remove 6K from it.
I'm with holding further comment on the Bursters at this time.