TLDR¶

I am trying to do a CSV import from a very old redmine install to a newer one.
I need the issue numbers to stay the same.
Every time I do the import, the process completes successfully, but all of the issue numbers are just autoincremented, starting at 1 (now ~500, because of repeated attempts).
I'm hoping there's some simple step I'm omitting.

Longer story¶

After creating some of the category and tracker data manually, and creating my users, everything imported ok.
When I exported from my old install, I chose "all columns".
When mapping values in the import wizard, *File Content Preview" shows the proper task numbers in the "#" field (the first field).

I selected the "#" field for "Unique ID". But the numbers just continue to auto increment:

Neither the old nor the new redmine install has any connection to our code repos.
But we still reference these issue numbers all over the place.

I googled to see if anyone else had the same issue, and found nothing.
All of the closely related problems I've seen on the forums are either very old or using a plugin (I'm just using the built-in Import feature), and none of them seem to mention this particular issue at all.

As I said before, we reference these issue numbers in lots of places.
It will add considerable difficulty if we have to adjust all of these references to point to new numbers for these existing tasks.

Old:

Environment:
  Redmine version                          2.0.3.devel.10073
  Ruby version                             1.9.3 (x86_64-linux)
  Rails version                            3.2.6
  Environment                              production
  Database adapter                         Mysql2
Redmine plugins:
  no plugin installed

New:

Environment:
  Redmine version                4.1.1.stable
  Ruby version                   2.5.8-p224 (2020-03-31) [x64-mingw32]
  Rails version                  5.2.4.2
  Environment                    production
  Database adapter               Mysql2
  Mailer queue                   ActiveJob::QueueAdapters::AsyncAdapter
  Mailer delivery                smtp
SCM:
  Git                            2.27.0
  Filesystem                     
Redmine plugins:
  no plugin installed