Hi Kooyeen, Though I understand your point, I don't think anybody would use the second sentence (I thought/knew it would have been be nice surprise for you ) to mean the same as the first in either pair. To me, " I thought it would have been be nice surprise for you" still tends to sound as if there was no surprise at all -- even in the context, so "would have been" wouldn't be good in the first pair either.
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Yankee To me, "I thought it would have been be nice surprise for you" still tends to sound as if there was no surprise at all --Agree