Depends on how units operate, but generally you have to
attempt IPPT every year. However if you fail while still under IHL,
you are exempted from RT.
My friends who who are instructors from BTMC can't even register
for IPPT as they are unitless and therefore, don't even have IPPT
while they are under IHL.
On the other end of the spectrum, my friends who came from Sungei
Gedong have to go for ICT every vacation period.
And wrong forum isn't it? 
