So people close to D4vd knew and/or knew of Celeste as his girlfriend of at least some amount of time, maybe even a few years' time. Some (all?) who have spoken about it since the body was discovered claim they thought she was a 19 year old university student before she died.
Which would STILL mean they knew she was very much underage up until recently, despite the fact that she was known to be in a girlfriend-boyfriend relationship with D4vd. Unless D4vd kept the relationship more secret in the beginning, I guess. He may have been trying to sell their background/origin story as him having only met her in the last year to year and a half or so, which would have made her not a minor, off limits to him as such,.
If so, I would bet that people in his crew and entourage, maybe even his fans, knew that this story wasn't entirely accurate, even if they did go along with it.