I've recently made three sets of flights and requested "RPU" and "GPU" upgrades when searching the flights. All three turns provided options, including flights where I'd get upgrades or waitlists. i'm actually using the RPUs/GPUs. Hurrah ;-)

Now, I've been trying to reserve flights for March and there are no dates or options for upgrades. Not one flight, page after page. (There are even flights with R9 / RN9 on the flight I'm interested in.) Not even the "waitlist" option.

Even MUA shows nothing.

This is just 2 months out. Are there restrictions I don't know about??