What should I do if there is existing filler remaining when getting fillers again in the same area?

I have had nasolabial fold fillers done once before.
Quite some time has passed, so I am looking into it again.

I have no way to check if it's completely gone, and
I am wondering if it is okay to add more while there is still a little left.

If existing filler remains
I would like to know if you are always supposed to melt it down and start over, or if there are cases where you add more depending on the condition?

For those of you who have had a similar experience, how did you proceed?

팔자필러는 시간이 꽤 지나도 일부가 남아 있을 수 있어서 무조건 녹이고 다시 하는 건 아니라고 하더라고요. 남아 있는 양이나 위치, 모양을 확인한 뒤 추가 주입이 가능한 경우도 있다고 해요. 오래된 필러라면 초음파로 잔여량이나 위치를 확인하고 상담받아보는 게 가장 안전할 것 같아요.

Botox/Filler

What should I do if there is existing filler remaining when getting fillers again in the same area?