This seems to be supported by ACER's designated 0-100 percentile range. The only way this is possible is by rounding:Yeh, I was under this same impression. It also kind of explains why I'd personally seen/heard of a lot more 99s/98s etc. compared to 100s during UMAT, given that UMAT 99 was actually 98.5-99.5, whilst 100 was 99.5+.
0 - 0.499th percentile = 0th percentile
99.5-100th percentile = 100th percentile
Also anecdotal evidence: four friends scored 99th percentile last year but no-one I personally know got 100th.