I haven't checked what gets publicised, but the various bylaws have said 500 metres for ages. eg.
Heaphy (in Kahurangi): http://www.legislation.govt.nz/regulation/public/2009/0014/latest/whole.html#DLM1679822
Abel Tasman: http://www.legislation.govt.nz/regulation/public/2009/0046/latest/whole.html#DLM1890614
Fiordland and Aspiring: http://www.legislation.govt.nz/regulation/public/1981/0065/latest/whole.html#DLM73706 http://www.legislation.govt.nz/regulation/public/1981/0066/latest/whole.html?search=ts_regulation%40deemedreg_aspiring_resel_25_a&p=1#DLM73753
I'm not sure what's happening now with the Lake Waikaremoana walk in Te Urewera, though, and I can't find any bylaws for Rakiura, which has only been a National Park since 2002.
It's confusing because it's always been set at 500 metres, but then when the Freedom Camping Act came in 7 years ago, it stated that all camping within 200m of a Great Walk was defined as Freedom Camping.
The Freedom Camping Act, in itself, doesn't make freedom camping disallowed within 200m of a Great Walk. It defines what Freedom Camping is (which is not all camping, such as camping in most of the conservation estate), and then makes it lawful for the relevant authority to declare camping as disallowed within that area. That's all handled in sub-part 2 of the FCA -- just remember that when it refers to "Freedom Camping" and how it can be restricted, it's not talking about the entire conservation estate... only the bits within a certain distance of a road, or a defined Great Walk. http://www.legislation.govt.nz/act/public/2011/0061/latest/whole.html#DLM3742867
So DOC could post an appropriate notice on its website that declares camping as disallowed within 200 metres of any Great Walk, but for most Great Walks it's already disallowed within 500 metres.
Penalties are slightly different, though. If you're fined under the Freedom Camping Act, for which they can just send an infringement notice, then there could be a fine of up to $1000 (or $200 if a fine wasn't specified). If you're caught under a bylaw, they'd have to convict you in court and then the fine could be up to $500.
As a side note, when the new Great Walks come in then someone's going to need to update the appropriate bylaws or amend Schedule 1 of the Freedom Camping Act, or the new ones won't have any camping restrictions. (Which mightn't be a problem unless it later becomes a problem.)