I have noticed that only handful airports in Serbia and Montenegro are covered.
SMATSA is their Air Traffic authority, and they are maintaining AIP data and publications; for example VFR AIP list of local airports, aifrields and heliports is VFR AIP (smatsa.rs)
In comparison, Romain airport data, published by Romanian AIRSO authority AIP Romania (aisro.ro) is included in Navigraph’s dataset.
It would be great if Navigraph and Simbrief included SMATSA airport and heliport data.