Today I have farmed for 6 hours without stopping. I dropped 4 u70 reds, 1 u70 white and 1 u70 green. (and one u70 blue)
Then I used the white and green stone in my +6 armor. Fail
Then I used the last 4 u70 reds in my +6 glove:
Fail
Success (because it was just one card)
Fail again
Success again (because it was just one card)
Result:
I lost 6 hours for nothing.