The emphasis nowadays is on 7 HKs + 10 ORNS years instead of 7HK+3LK, impact being you don't necessarily have to serve 3 LKs. Activities which count towards ORNS are ICTs, Mob Mannings and passing IPPT, according to ns.sg (
https://www.ns.sg/web/portal/nsmen/home/nstopics/orns/article/overview-orns/types-orns-activities)
I have mates who MR'ed with 7HKs/2LKs, but 10 ORNS years fulfilled. That 1 work year where we had no ICT, there was a briefing which not everybody was called up for but counted as 1 ORNS year for those who attended.
Unfortunately for those who did not get called up for the briefing, they are stuck at 7HKs/2LKs and 9 ORNS years, they will eventually MR in FY19/20 with 8HKs/2LKs, 10 ORNS years.
I was lucky to have deferred one HK ICT but somehow my ORNS is also at 9 years as of FY18/19, i believe a mob manning that same year "saved" me. So if everything goes well i will MR with 7HKs/2LKs and 10 ORNS fulfilled in FY19/20. We already know the ICT dates.