IS the software level listed on PCM, if so what would it be for updated? Or when I check with scanner?

Might just be sooting up during idle, if so, then may be the MAP. Check the reading

Huh, missed the year. ‘09 shouldn’t have that issue as even my ‘03 had the updated programming from Merc. It would only soot a very small amount in the spring when water and air temps were cold. Otherwise no soot at all.

Is this sooty transom a new issue? Running 90 octane on a stock HO is alot of your problem. If it's an 09 HO you have the updated PCM fuel table. No reason to mess with that. If it's a new issue I would comfirm fuel pressure at rail. Should be 42-3psi KOEO. If higher, look into your fuel system contaminated from paint from the Gen 3 cool fuel box. It restricts the regulator, injectors, pump screen pickup and can cause fuel psi to spike and overfueling is result.

Early 496HOs did have either a reprogram from Mercury or a whole ECM replacement, which helped with the sooting issues.
Ensure that your ECMs have the latest software update by talking to your Mercury dealer.

The colder it is, the more they soot. Spring and Fall were worse than hot summer months.
Mine ran the cleanest on 87 octane. Anything else sooted the transom noticeably more.

I'll again emphasize run good quality 87 octane only. Higher octane will soot and is a waste of money on that motor in stock form. I run Shell 87 and have zero soot on the transom. I had to slum it one weekend and put marina 91 and had soot, not kidding.

did mercury publish a bulletin, if so what's the number?

Same here, mine had a little soot when the water was cold. Ran plain old 87 pump gas in mine. Ran great! Mine was a 2005 model.