I'm TCQG, and I always fly on discounted youth fares. So far, on all flights since the start-up of Swiss to and from the US (8x), without exception, I have been in C-class due to overbooking of the Y cabin. In addition, I had two operational upgrades on Avros to Hamburg.
Most european flights usually aren't full - but longhaul to US usually are, especially during the summer months when I fly ...
I do consider myself very lucky, though.