How do I log this?

I personally would not worry about it. I try to be careful to log everything but there are occasionally some things like that that you will run across. I think it all works out in the long run. If I am over a couple of calories or carbs here, I'm probably under a couple somewhere else. I think basically this is just a good guideline. I've looked up items and found them listed several times and some of them list different calorie counts or carb counts. Best of luck and good for you for wanting to be accurate and asking questions. That is what this site is all about.

If you know how much you started with, you could measure what's left in the bag and log the difference. I wouldn't worry TOO much about it though, I doubt a marinade would add a significant amount of calories, but I understand the desire to be accurate.

This, I do this when I marinade stuff, the meat soaks up some, just not all.