I don't think the reference letter from principal can be considered in the application for P.1. Though no such reference letter can been obtained from principal for my kid, my kid is accepted by our dream school as well as other famous schools. So you don't expect too much for such letter. Take it easy.
The Kindergarten Principal's reference may not be of much use so don't spend much time on cosmetic stuff. Save the time to read a book to your child will be more meaningful.