If something is worth or could be deemed by others to be worth €1,000,000 and someone estimates its worth at €950,000, that is an approximate valuation.
If they say it is worth €950,000 +/- €50,000, it is still an approximate valuation, but with a deviation.
The "fourchette" (price bracket?) in this case is €900,000 to €1,000,000. While the fourchette IS an approximation, I suppose, it is both less of an approximation since it is more likely to encompass the actual value, and more of an approximation since it covers a greater range, or at least the range is stated, which in turn makes it less of an approximation.
It probably doesn't matter, unless your text is likely to run into a problem by calling €900,000 to €1,000,000 an approximate valuation when it is in fact a valuation range, even an approximate valuation range.
I think I have answered your question, approximately.
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