Just out of curiosity how do you know you gained 12 lbs of solid muscle or lean mass if I am understanding your meaning correctly? And also when did you start your PCT after your cycle? Also I do not see HCG in your PCT regiment. Are you not using any? If your not on HCG I have to ask why since neither Nolvadex nor Clomid have a drastic impact until 14 days into PCT where 2500 iu's every other day of HCG drastically impacts HPTA function and limits the production of cortisol by bring natural test production up as soon as possible thereby bringing the body back into homeostasis. The HCG is typically run for 16 days and then no more on a PCT too much of it for too long starts to reverse the HPTA cycle. However, I have heard of guys doing low doses all through there cycle to keep HPTA production functioning properly eliminating the need for such an aggressive PCT program.
I tend to agree with Goth on this in that you can only expect to keep 30-50 percent of your gains every cycle. I think anavar was tested to show that older men and younger boys kept the lean muscle mass the longest and that was while on a regular healthy diet and no lifting.

I feel your pain. If everyone held onto their gains each time, people would be the size of rhino's.
wouldnt be nice to gain like 10 lbs a cycle x 15 cycles and in 6 years weigh 350lb of solid muscle. It'd be nice.

When you come off juice, you lose muscle-----that's how it works.
If your lucky, you'll keep 5-6 pounds of what you gained for a while, but even that will be lost if you don't eventually cycle again, assuming you have already reached your genetic potential.