the control center chokes on initial number in user name

Thank you for taking the time to report this bug and helping to make Ubuntu better. The issue you are reporting is an upstream one and it would be nice if somebody having it could send the bug to the developers of the software by following the instructions at https://wiki.ubuntu.com/Bugs/Upstream/GNOME. If you have done so, please tell us the number of the upstream bug (or the link), so we can add a bugwatch that will inform us about its status. Thanks in advance.

Status changed to 'Confirmed' because the bug affects multiple users.

I come from just trying to document the same bug (I searched first to check something similar but did not find it)

The GUI to add a user in Ubuntu allows a username beginning with a number
  (checked appears ok but call to user creation fails).
  The reason is that the called Perl script adduser does not accept it. This script is configurable in /etc/adduser.conf:

  # check user and group names also against this regular expression.
  #NAME_REGEX="^[a-z][-a-z0-9_]*\$"

  As it is commented out, (same) value is taken from
  /usr/share/perl5/Debian/AdduserCommon.pm:

  $configref->{"name_regex"} = "^[a-z][-a-z0-9_]*\$";

  To solve this, you could:

  - validate only names matching the expression.

  - modify /etc/adduser.conf with another NAME_REGEX to fit Ubuntu's policies
  (in this case, adduser would be affected, too).

  Added to this, in a root terminal, adduser/passwd allow any password.
  This GUI limits this possibility (for security matters, that is ok, but IMHO user creating an account from GUI should behave "like root").

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: gnome-control-center 1:3.28.2-0ubuntu0.18.04.6
  ProcVersionSignature: Ubuntu 5.3.0-42.34~18.04.1-generic 5.3.18
  Uname: Linux 5.3.0-42-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7.12
  Architecture: amd64
  CurrentDesktop: ubuntu:GNOME
  Date: Fri Apr 24 11:59:24 2020
  ExecutablePath: /usr/bin/gnome-control-center
  InstallationDate: Installed on 2020-03-10 (45 days ago)
  InstallationMedia: Ubuntu 18.04.4 LTS "Bionic Beaver" - Release amd64 (20200203.1)
  SourcePackage: gnome-control-center
  UpgradeStatus: No upgrade log present (probably fresh install)