Do you have an update?

This seems correct to me, however, then also the output for
 "POSIX upper limit on argument length (this system)"
should be fixed, too, because that should reflect the
original limit without 'size_of_environment' already being
subtracted. This amends to:

diff --git a/xargs/xargs.c b/xargs/xargs.c
index 89e78a3..673fdc0 100644
--- a/xargs/xargs.c
+++ b/xargs/xargs.c
@@ -696,13 +696,13 @@ main (int argc, char **argv)
              (uintmax_t)bc_size_of_environment ());
       fprintf (stderr,
              _("POSIX upper limit on argument length (this system): %" PRIuMAX "\n"),
-             (uintmax_t)bc_ctl.posix_arg_size_max);
+             (uintmax_t)bc_get_arg_max ());
       fprintf (stderr,
              _("POSIX smallest allowable upper limit on argument length (all systems): %" PRIuMAX "\n"),
              (uintmax_t)bc_ctl.posix_arg_size_min);
       fprintf (stderr,
              _("Maximum length of command we could actually use: %" PRIuMAX "\n"),
-             (uintmax_t)(bc_ctl.posix_arg_size_max - bc_size_of_environment ()));
+             (uintmax_t)(bc_ctl.posix_arg_size_max));
       fprintf (stderr,
              _("Size of command buffer we are actually using: %" PRIuMAX "\n"),
              (uintmax_t)bc_ctl.arg_max);