I believe around 95 clears you should have a 100% drop rate.
Also remember it only counts the 1st clear on each character for that week. I've seen a lot of people complaining and it turned out they were farming the raid multiple times a week on the same character, because they thought it boosted the odds for next week.
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That was an issue with EoT when it only counted 1 looted clear for the drop rate increase & not every looted clear each week. Bungie acknowledged this & "fixed" it so that all looted clears counted towards the increased drop rate. Vex has no increase drop chance after clears so it doesn't matter how many times you clear it your chance of getting it is still the same. For me it took 32 looted clears.
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Don't know where they got that idea