Can easily hack the URL from the template for the beta version:
The key thing is the hex number and the version number of the release. This can be found by looking at the links on the download archives page.
Also looks like netstorage.unity3d.com/unity is interchangeable with download.unity3d.com/download_unity.
Based on a random sampling, the docs (and therefore the API) don't change between patch releases, only minor releases. It's safe to take the latest patch release of any version to use to generate the API data.
Prior to 5.3.0, documentation was packaged with the UnitySetup64.exe. If you want to get it, download these massive files, extract with 7-zip and get at the Documentation folder.
- 5.2.5 - 1 Jun 2016
- 5.2.4 - 16 Dec 2015
- 5.2.3 - 19 Nov 2015
- 5.2.2 - 21 Oct 2015
- 5.2.1 - 22 Sep 2015
- 5.2.0 - 8 Sep 2015
- 5.1.5f1 - 7 Jun 2016
- 5.1.4 - 6 Oct 2015
- 5.1.3 - 24 Aug 2015
- 5.1.2 - 16 Jul 2015
- 5.1.1 - 18 Jun 2015
- 5.1.0 - 9 Jun 2015
- 5.0.4f1 - 6 Jul 2015
- 5.0.3 - 9 Jun 2015
- 5.0.2 - 13 May 2015
- 5.0.1 - 1 Apr 2015
- 5.0.0 - 3 Mar 2015