That would be my guess. Of course in TW2000 you would be breaking all the old SLRs out of storage to arm up the 3rd wave replacements, home guard...etc
Use of SLRs in Twilight 2000 would not be an issue - L85 reliability issues did not become a PR/military problem until 1991 and were not used in infantry conflict until the 21st century. The reliability upgrades would not have existed when the Twilight war began, so stocks of reliable weapons with plentiful existing ammunition would have been rushed to the front.
And before anyone points and laughs at L85, can you imagine the US fighting a War* during the period that the M16 was being introduced continuing to issue them to replace the M14s? Reputational damage and commercial interests be damned.
* Vietnam was a meat grinder, great for testing, not so much for those doing the testing.
Now back to the programme...