I think a couple of the Sigma guys haven't logged in here for a while, they may be busy or on vacation. I don't know anything about the different models, sorry. Nearly all of the NLG website is free access but the download area requires a contribution to the website for access, that is a way to help pay the costs to keep NLG online. The donation can be practically any reasonable amount, see the info near the bottom of most NLG webpages for details. The other website I gave link for earlier has a good selection of manuals but as you said it can be hard sometimes to know what manual is for your machine. The idplate is not always as informative as it should be.
Here is a screenshot of the Sigma manuals in the NLG download area. Maybe you can see if the manual you are looking for is there: