The bills

Conyers bill of Feb 2003 (H.R.676):  "U.S. National Health Insurance Act (or the Expanded and Improved Medicare for All Act)" — 38 co-sponsors

• establishes a national health program for all US residents
• various other stipulations changed since then 

https://www.congress.gov/bill/108th-congress/house-bill/676

Sanders bill of Dec 2013 (S.1782):  "American Health Security Act of 2013" — no co-sponsors

• eliminates Titles XVIII (Medicare) and XIX (Medicaid)
• repeals provisions of the AFA (the exchanges) 

https://www.congress.gov/bill/113th-congress/senate-bill/1782

Conyers bill of Jan 2017 (H.R.676):  "Expanded & Improved Medicare for All Act" — 24 co-sponsors

• to cover all US residents with free health care (all spelled out)
• only public or nonprofit institutions can participate 

https://www.congress.gov/bill/115th-congress/house-bill/676

Sanders bill of Sept 2017 (S.1804): “Medicare for All Act of 2017” — 16 co-sponsors

• establishes a national health insurance program to cover all US residents
• over specified items and services
• be fully implement in four years 

https://www.congress.gov/bill/115th-congress/senate-bill/1804/

Jayapal bill of Feb 2019 (H.R.1384):  "Medicare for All Act of 2019" — 118 co-sponsors

• establishes a national health insurance program administered by the DHHS
• to cover all US residents with free health care (all spelled out)
• terminates health insurance exchanges
• establish implementing provisions relating to provider partipation,
• admin, pyaments and costs, negotiating drug prices
• be fully implemented in four years 

https://www.congress.gov/bill/116th-congress/house-bill/1384

Sanders bill of April 2019 (S.1129):  "Medicare for All Act of 2019" —14 co-sponsors

Matches House version H.R.1384, sort of
https://www.congress.gov/bill/116th-congress/senate-bill/1129

Text has never changed, but Politico reported in Aug. 2019 that Sanders said "companies with union-negotiated... coverage would have to renegotiate their workers' contracts [to be overseen by Natl Labor Relations Bd] ... any resulting health care savings from the single-payer system would be required to be returned to workers in the form of higher wages or more generous benefits."  

Important differences (particularly on cost containment) described by Lambert Strether in Naked Capitalism:

Representative Jayapal’s bill, HR 1384, meets the definition of a single-payer bill as originally outlined in PNHP’s 1989 article and as most experts define the term. It contains the four elements of a single-payer system: It relies on one payer (HHS, not multiple payers called ACOs) to pay hospitals and doctors directly; and it authorizes budgets for hospitals, fee schedules for doctors, and price ceilings on prescription drugs.

Senator Sanders’ bill contains two of those four elements – fee schedules for doctors and limits on drug prices. That’s a good start. He should add the other two. He should get rid of Section 611(b), the section that authorizes ACOs, and thereby ensure HHS is the single payer. And he should add a section authorizing HHS to negotiate budgets with each of the nation’s hospitals.