Captain Blood, and everyone else,
It is very hard to run a multi-round tournament of this kind. Here are a couple of suggestions from my experience:
Randomly pick the match-ups for the first 6 rounds, only adjusting if you accidently get a rematch..
The last three weeks become a round robin for each group of four so
Group A is 1 to 4 from the first 7 weeks
Group B is 5 to 8
Group C is 9 to 12, etc
Feel free to adjust the bottom group or two if you have an odd number in the last group
Each group them play each member once in the last 3 weeks so the final 3 rounds for Group a would be:
Week 8 Week 9 Week 10
1 vs 4 1 vs 3 1 vs 2
2 vs 3 2 vs 4 3 vs 4
It is OK for rematches to occur in the final 3 weeks - this will only happen if two players in the same group happened to play in the first 7 weeks.
This format ahould make your life MUCH easier and is likely to give a clear winner.
What do you think?