Commentary.
The phrase "on Monday" indicates to me that you saw him that day. If I wanted to say "I will see him before Monday" I would use by and not on.Part 1:
Consider:
A-I will have seen him on Monday.
Isn't this sentence ambiguous. I think it could mean two things:
1-I will see him before Monday.
2-My seeing him will have taken place on Monday.
(You are going to see him on Tuesday. But I'll have seen him on Monday. I will have seen him on Monday, that is before you see him on Tuesday.)
Is this analysis correct?
Part 2:
Could the sentence:
B-I had seen him on Monday.
mean that I saw him before Monday?
Consider:
C-I had already seen him on Monday.
8)

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