Just something I experienced when filling out forms

I quit my previous job and joined my current job about a week ago. They were asking me to fill out a onboarding form (English form). In one of pages it is asking me about the final salary date. One of the field is asking retirement date. I went to my previous company to ask HR about it, but they don't know. I went to my previous boss and he didn't know either. I was so confused and starting to search Google and all I got was to check pension handbook, but that is only saying age not date. I was sooo confused so I called my new company hr, and it turns out the so called retirement date is the date of termination (退職日).