No one is guessing here. Just take a look at this link: https://quochoi.vn/bandannguyen/cutriQH14/Pages/Home.aspx?ItemID=33149

The Vietnam Ministry of Transport has decided to reroute QL.20 to Mimosa Pass in 2016. If it was still part of the National Route, the Ministry would be responsible for its recent upgrade, not the government of Lam Dong Province.