DPO and testing

Elle

Anyone know if there’s any reason documented why some seem to be able to get a positive pregnancy reading (so enough hcg) at 9DPO etc (many seem to have said it in this forum anyway) and others cannot until AF is due or 13DPO or later? It looks like they’re using the same tests by the photos

My first everything was negative until 13DPO

2WW feels like forever when you just want to know 😫