Well, so if you checked all these datas you still don't know 90% of all factors for the takeoff performance calculation.
Just some examples.
- which takeoff performance program for calculation did they use?
- how much cargo did they have?
- where is the c.g.?
- improved climb yes/no?
- does this acft in particular has the alternate forward c.g. option available?
- what was the ZFM?
- how much fuel?
- takeoff configuration? (bleed air etc.)
- technical defects? (e.g. antiskid inop)
- intersection takeoff calculation?
- did they calculate with the real weather data or did they calculate with some "margin"? (e.g. choosing less or no headwind component)
- and which captain was flying and how's his preferences for takeoff calculation? (same airport, same situation, different captain = different t/o calcs, like "no flex temp, no improved climb, no alternate forward c.g. option")
So its just always the same answer - you don't know, you cannot know, you will most probably never know. best would be: maybe you can manage one day to join a flight in the cockpit and join the takeoff calculations?
Anyway, enjoy spotting!