Reading this a little late, but I'll bite...
Getting back to basics, it's best to revisit "quantile" definitions. However, therein lies the problem; there is NO single accepted standard definition. Even statistical software, for example SAS, offers you to calculate quantiles using one of 5 definitions. So before you begin you need to accept the definition you are comfortable with.
I’ve always taken the view that quantiles are points, not ranges. They represent the points that divide a data set equally. There are 3 quartiles which have the effect of creating 4 ranges. There are 9 deciles creating 10 ranges and 99 percentiles creating 100 ranges. Because of this, there is no 100th percentile. Some software does reference the 0th and 100th percentiles BUT this is simply the software equating them to be the mathematical minimum and maximum respectively.
With your particular example; it’s problematic BECAUSE you have fewer values than percentiles. There are 2 possible reasons you have be on the 100th percentile:
1. It has been equated to equal the maximum value (which is not a true percentile as discussed above)
2. It is the result of a rounding calculation…due to