The requirements vary from state to state. Scan the entire file for any needed future reference.  Our office no longer retains paper files.

Legally I'm required to keep listing agreement & disclosure (if our listing), signed sales agreement and closing statements.  But I also keep all notes from agents, copy of plat, copy of MLS sheet, 

Time to check with the New York State real estate commission. They make the rules for record keeping.

Each brokerage probably has different rules. I can tell you that for all my closed files, I keep every form that was signed (disclosures, etc), a copy of any offers made, a copy of the MLS document and the confirmation pages for showings.  Our office also has all "required" documents on our dotloop electronic system. I probably keep more than I need to, but hey, you never know when I might need something.

Construct your question in a more precise manner.

The responses will then be more consistant.

Example: "What does the State of New York require the BROKER to retain for each completed transaction of residential real estate?"

I agree it will depend on state laws.

Typically, the state real estate commission will outline what you do need to have in file and for how long. You might check there.

rely on your broker's answer. They are the ultimately the ones responsible. 

Our state real estate commission spell out what we must keep.

It depends on a state laws, then your broker may have different additional requirements.

Each brokerage has its own system and require certain docs. You wish to joint a paperless company with minimum amount of redtape and good compliance officer.  A bad compliane offier can hold your commission check and make you do it over and over and charge you for it.....

On smaller borkerage they want everything and anything, hard copy filed and retain in boxes for 7 years. They even charge you for printing endless docs, HOA minutes... Stay away from them too.

Great answers you got for your question.

We keep most everything.