WOW!! I'm sure glad it was you that had to pass that 7.5mm stone on your own 8 months ago and not me!! LOL! That's a pretty good sized stone to pass on your own!
As to your question, in all my 30 plus years of suffering with these stones, of all sizes, I have never had one where there wasn't blood in my urine to confirm that I had a stone. I have had cat scans misread and was told I had no stone(s) when in fact I had three of them at the time the cat scan was done. A kidney stone certainly doesn't have to be as big as 7.5mm to cause you severe pain, but with no blood found in your urine AND a negative cat scan, your pain might not be caused by a kidney stone. Why not wait a short time and have both re-done to see if anything shows up the second time in either test. If not you'll know and can go from there looking at other possibilities for your pain. If positive on either test, then you'll know that way too, for sure. Good Luck and please let us know what you find out.
My current plan is to wait things out and drink as much water as I can. I'll update as things go