There is no I inventory available on any of the flight to AMS on 10/8. Is the chance of an upgrade better if a flight is booked on a busier flight or one that is less busy based on information from the availability tool (see below)?

Northwest Airlines 40
Airbus A330 4:05 pm
Detroit, MI (DTW) 5:55 am (Next day)
Amsterdam, Netherlands (AMS) J9 C9 Z0 I0 Y9 B9 M9 H9 Q9 V9 L9 T9 K9 non-stop 3940 7:50
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Northwest Airlines 68
Airbus A330 5:45 pm
Detroit, MI (DTW) 7:35 am (Next day)
Amsterdam, Netherlands (AMS) J9 C2 Z0 I0 Y9 B9 M9 H9 Q9 V9 L9 T9 K9 non-stop 3940 7:50
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Northwest Airlines 54
Airbus A330 7:10 pm
Detroit, MI (DTW) 9:05 am (Next day)
Amsterdam, Netherlands (AMS) J9 C5 Z0 I0 Y9 B9 M9 H9 Q9 V9 L9 T9 K9 non-stop 3940 7:55
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Northwest Airlines 48
Airbus A330 9:25 pm
Detroit, MI (DTW) 11:15 am (Next day)
Amsterdam, Netherlands (AMS) J9 C9 Z0 I0 Y9 B9 M9 H9 Q9 V9 L9 T9 K9 non-stop 3940 7:50
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You're 60+ days out and, as such, I think they may release seats into I as time progresses. Keep an "I" on it daily. (Aww, I'm so pun-ny )

I will do this, but was wondering if there are any flights that I seats might be more likely to be released based on other availability tool information (e.g., flights 68/54 have 2 and 5 C bucket seats available vs 9 for the other two flights).

a few things you can try are: open avail for 20 plus flights 2+ stops, different routing say via mem, different european destination. etc. sometimes theres no avail to ams, but if you search for brussels there is avail and its on the same plane, go figure hope this helps.