Secret Clearance--border patrol

At what point are the medical records requested, if at all, and what if the records do not go back markedly far in my possession now? Do I need to work with the investigators to try to track down the full record? Is the physical sufficient to pass? What is the name of the medical form

How is the Top Secret Clearance different from the sf86? The website says this is a tier 5 investigation. Can you elaborate on this process, particularly how tier 5 or Top Secret Clearance overlap, if at any? Why do so many people fail the polygraph test and how is it 4-6 hours? (I read a 2016 article stating 2/3rds of applicants failed.)

From my understanding, investigation, using sf86, would be, via INV 40-43 forms, criminal and credit records, SSN based employment verification via sending said forms to educational institutions about possible misconduct, and sending similar forms to past employers? What if one cannot get a past manager or coworker to talk about work at previous employers? Can HR at said locations fill this role? I have not kept up with several employers. Thank you for your support.

In such a situation, or alternatively, in a situation where the supervisor information I provide, refers the investigator to HR as a matter of policy (this is common, for instance Walmart has such a policy), what is the investigator apt to do–ask for another contact at the company, get me to sign more release forms, or just move on to the next employment listing on sf86 tier five?

This is a very important question to me, as I am approaching the cut off age for the position and I have several problems with past supervisors like this.