If I'm not mistaken the \renewbibmacro*{name:last-first}[4] block

\renewcommand*{\revsdnamepunct}{}

It's really nice to see some development here.

While I was reading the documentation for v0.5 I realised that the date on the title page still says "2011/09/09". That might confuse people. I suggest to change that to the current date for the next release.

Furthermore the documentation claims

This package was tested with \biblatex verson 1.6.

If I'm not completely mistaken the recent update uses functionality of v3.8, so that should probably be changed. I tested the package with the current biblatex version 3.12 and it seems to work so far, so maybe that number can be bumped up.

I also noticed that the package is author-maintained as per LPPL (https://www.latex-project.org/lppl.txt) author-maintained packages are problematic, since it becomes harder to pass on the maintenance of a package to other people. Maybe it would be possible to ask @marcodaniel to waive this status.

I have also found a number of smaller issues that might be worth discussing. Would you prefer if I opened several small issues for those or one large "collection" issue?

The documentation quotes the full NEJM style reference. Apparently there have been some subtle changes to the requirements since biblatex-nejm was first released. The documentation has

4. U.S. positions on selected issues at the third negotiating session of the Framework Convention on Tobacco Control. Washington, D.C.: Committee on Government Reform, 2002. (Accessed March
   4, 2002, at http://www.house.gov/reform/min/inves_tobacco/index_accord.htm.)

but https://www.nejm.org/author-center/new-manuscripts has

4. Medicare: trends in fees, utilization, and expenditures for imaging services before and after implementation of the Deficit Reduction Act of 2005. Washington, DC: Government Accountability Office, September 2008. (http://www.gao.gov/new.items/d081102r.pdf.)

Note how the older version includes the access date of the URL and the new one does not. Is there any indication in newer published NEJM papers that the access date might still be required?

Following on from that, note how

makes use of the addendum field. In biblatex, the preferred way to give the URL is the url and urldate field.

If there is a decision on which format to follow for @online I can try to come up with a small pull request to that effect.

Description of Issue

The current version of biblatex-nejm inserts a comma after the family name (last name) of each author. However, the examples of formatted references on the NEJM website do not include commas after the family name.

Minimum Working Example (MWE)

Step 1: Put the following into a file called example.tex:

\documentclass{article}

\usepackage[backend=biber, style=nejm]{biblatex}
\addbibresource{mybibfile.bib}

\begin{document}

First citation: \cite{Kuczmarski2000}. Second citation: \cite{usposition2002}. Third citation: \cite{Goadsby2001}. Fourth citation: \cite{Shapiro2000}.

\printbibliography

\end{document}

Step 2: Put the following into mybibfile.bib:

%% Examples for biblatex-nejm
@ARTICLE{Shapiro2000,
author   = "A.M. James Shapiro and Jonathan R.T. Lakey and
Edmond A. Ryan and Gregory S. Korbutt and Ellen Toth and
Garth L. Warnock and Norman M. Kneteman and Ray V. Rajotte",
title    = "Islet transplantation in seven patients with type 1 diabetes
mellitus using a glucocorticoid-free immunosuppressive regimen",
journal  = "N Engl J Med",
year     = "2000",
number   = "2",
volume   = "343",
pages    = "230-8"
}
@ARTICLE{Goadsby2001,
author   = "Peter J. Goadsby",
title    = "Pathophysiology of headache",
journaltitle = "Silberstein SD, Lipton RB, D'Alessio DJ, eds",
journalsubtitle="Wolff's Headache and Other Head Pain",
location = " {Oxford, England}",
publisher= "Oxford University Press",
edition  = "7",
year     = "2001",
pages    = "57-72"
}
@ONLINE{usposition2002,
title    = "U.S. positions on selected issues at the third negotiating
session of the Framework Convention on Tobacco Control",
location = " {Washington, D.C.}",
publisher= "Committee on Government Reform",
year     = "2002",
addendum = "(Accessed March 4, 2002,
\url{http://www.house.gov/reform/min/inves_tobacco/index_accord.htm})"
}
@ARTICLE{Kuczmarski2000,
author   = "Cynthia L. Ogden and Robert J. Kuczmarski and Katherine M. Flegal
and Zuguo Mei, MD and Shumei Guo and Rong Wei and
Laurence M. Grummer-Strawn and Lester R. Curtin and
Alex F. Roche and Clifford L. Johnson",
title    = "CDC growth charts: United States. Advance data from
vital and health statistics. No. 314",
journaltitle  = "National Center for Health Statistics",
location = " {Hyattsville, Md} ",
year     = "2000",
addendum = "(DHHS publication no. (PHS) 2000-1250 0-0431)"
}

Step 3: Run the following commands:

pdflatex example
biber example
pdflatex example
pdflatex example

Step 4: Open the file example.pdf in your favorite PDF viewer. This is the result:

The accessed date for URLs is ignored.

It can be added back in using the technique described here.

For instance:

\DeclareFieldFormat{urldate}{%
  [Accessed\addspace%
  \mkbibmonth{\thefield{urlmonth}}\addspace%
  \thefield{urlday}\addcomma\addspace%
  \thefield{url year}]}

(This would need to be tweaked a bit to match the NEJM URL format.)

At the moment the documentation uses @article to format a reference that is clearly an @incollection

Not only is that theoretically unsatisfying, it severely inhibits portability of .bib files for biblatex-nejm.

Given the required output, biblatex-nejm would probably have to include a modified driver for @incollection.