When I was a CPT in the Army, I went through the AVOAC (Aviation Officer Advanced Course) with an Indonesian Major. At the time they had M16's and BHP's. This was back in the 80's, so the locally produced FNC may well have replaced them all.
They were a "non-aligned" nation. So they gravitated towards both sides depending on the domestic politics of the age. As a result, they ended up with a pretty eclectic bunch of shit over the years which is how they wound up with some AK-47/AKM, some FAL's, some G3's, some of this and some of that, etc. They kinda settled down in the late 70's and started buying M16A1's from Uncle Sam in sizeable batches every couple years. In the mid-80's, they went with the FNC, buying the first batch from FNC and then signing a license for local production in 1984.
They've done a better job at "standardization" than most countries. Most places run all sorts of stuff and have a logistics nightmare going on.