Skills Assesment - Deducted 4 years from my working experience

I'm 35 years old and passed my skills assessment recently from ACS - Australian Computer Society.

After the graduation, I started working from Nov' 2012 ( so nearly 10 years of experience as of now) but, they have counted my experience since Nov' 2016!! (Deducted almost 4 years). They didn't mention any reason and my documentations were perfect.

1. Is this normal?
2. How can check the reason for the deduction?
3. Can I appeal? how?
4. What else can I do?

Appreciate if anyone could assist..

Thank you!