In article ,
David Damerell wrote:

Quoting :
Michael Press writes:
No, changing the subject header does not change alter the threading.
Speak for your own news reader. Tin, the UNIX threaded news reader
that I use, keeps threads by title

No; you are misusing the term "thread". A "thread" is a group of articles
associated because of Message-IDs and References lines.

What tin does is group-by-Subject, which is inferior to true threading.
The answer is to get a newsreader which functions correctly.

That is what Tin does by default, but Tin can sort by references.
In the man page under
GLOBAL OPTIONS MENU AND TINRC CONFIGURABLE VARIABLES
is a configuration variable for sorting articles
by the References header.

Thread articles by (thread_articles)
Defines which threading method to use. It's possible to set the
threading type on a per group basis by setting the group attribute
variable thread_arts to 0 - 4 in the file ${TIN_HOME-
DIR-"$HOME"}/.tin/attributes. (See also "GROUP ATTRIBUTES".) The
default is Both Subject and References. The choices a

0 None, don't thread.

1 Subject, thread on ''Subject:'' only.

2 References, thread on ''References:'' only.

3 Both Subject and References, thread on ''References:'' then
''Subject:'' (default).

4 Multipart Subject, thread multipart articles on ''Subject:''.

5 Percentage Match, thread base upon a partial character match on
''Subject:''.

--
Michael Press