I started doing single player. I took a seed with the exit near the waypoint on the durance and got a go at mephi.

I did 600 runs at P3 with 350 mf. Now i know those surely are far from enough to guarantee a stormshield or shako drop. But i am getting a bit distrusting of this whole seed thing.
Would it be possible to have a seed that will simply never drop the items i want ?