Need advice 360 timing chain cam/crank slightly off

It`s been about 15 years since I put a new timing set on the 340.
I set tdc #1 verified on timing mark.
Old set was at 12 and 6.
New set at 12 and the only way the cam sprocket would match the key was at 12 now. I was like:wtf: I assembled any how and was good to go, runs great. Still can`t wrap my head around that deal.