Good reason for Backdate request form for EI

Hi,I was laid off this April, and I was misguided by some information on line said whenever I apply for EI, the time is start from the date i laid off, not from the date i applied. So I did not file for EI application until July.
Now I got my EI money, it is not from April.
Somebody said I still could get my EI back, just fill out Backdate Request Form, but I got have a good reason.
Can anybody tell me what reason should i use?
Three months EI is a big money for me, I do not want to loose it.
Thank you very much!