ESF - Kln Junior School

My son is studying nursery class in Anfield, and I am thinking about his primary studies recently. My initial plan is to put him straight to Anfield primary, but they only accept 50 students each year. Anfield kinder do have priority for interview but not guarantee a seat, so that's why I am thinking about more options. One of my plan is to apply for Kln Junior, and I notice there is always difficult to get in with the reasons of its popularity as well as priority also given to existing Esf kinder. Could I apply earlier like this year for my son entering Kln junior in 2020 Or any other suggestions?
TIA