**********GROSSOUT WARNING****************
I can share what little I know. In general, the hotter the ambient temp, the faster the rate of decomp. Iowa summers can get pretty hot. I think earlier mention about mild climate there may have been talking about later in the year, not the summers. By 5 weeks, there might be some really good ongoing liquification (MOO), but the shade and coolness between the rows and under leaf/stalk clutter could slow that down some.
Insect activity comes in waves, and the players change as time passes. Insect activity also can increase body temp, to the point that it can be detected on infrared. Also, the higher the ambient temp, in general, the more insect activity. Bugs might like it in the shade, under leaf clutter.
The effect of stab wounds depends on where. Penetrating abdominal wounds that perforate the gut (small intestine especially) will release gut bacteria and possibly speed up decomp (again, MOO), and will help to slowly release gases associated with putrafication (the breakdown of proteins) and decrease bloat. I think that liquification is associated more with fatty tissues and internal organs. The fatter the corpse, the bigger the soup; the more soup the more liquid substrate for bacterial growth. If you cut up and lacerate the liver and pancreas, those enzymes released into the abdomen should speed up decomp. Any stab wound (the bigger the better) will allow increased insect egress into the body and thereby increase rate of decomp, especially by allowing for increased internal maggot activity (I think). By the way maggots only eat dead flesh, they were meant for this.