Has something changed or were you never able to download programmes within iplayer but listed as "This programme is not currently available on BBC iPlayer" ?  I could have sworn I used to be able to download these items using --pid= even if they were showing as unavailable

Seems now you can only download stuff that could do using an index number ?

Example - 

C:\Users\Becky>get_iplayer --pid=p043ldkg
get_iplayer 2.99-windows.0, Copyright (C) 2008-2010 Phil Lewis
  This program comes with ABSOLUTELY NO WARRANTY; for details use --warranty.
  This is free software, and you are welcome to redistribute it under certain
  conditions; use --conditions for details.

  NOTE: A UK TV licence is required to legally access BBC iPlayer TV content

INFO: Episode-only pid detected
INFO: Trying pid: p043ldkg using type: tv
INFO: Trying to download PID using type tv
INFO: pid not found in tv cache
Matches:

INFO: 1 Matching Programmes

WARNING: No programmes are available for this PID with version(s): default


[color=#ffffff][size=x-small][font=Arial, Helvetica, freesans, sans-serif]SThi[color=#ffffff][size=x-small][font=Arial, Helvetica, freesans, sans-serif]This programme is not currently available on BBC iPlayer[/font][/size][/color]s programme is not currently available on BBC iPlayer[/font][/size][/color]

You can't download programmes that are not available, and never could. Sort of a tautology, really.

I must have dreamt it then!  That said though, there are programmes listed in the iPlayer webpage itself that I can obtain using --pid= but aren't listed if I search for the same programme  by names so...

C:\Users\Becky>get_iplayer "the paras"
INFO: 0 Matching Programmes

But it works if I use --pid= reference obtained from the iPlayer url http://www.bbc.co.uk/iplayer/episode/p00...80-platoon

This programme is listed as 'archive' so are archive programmes excluded from the get_iplayer programme search ?

Read the FAQ section on searching