Timber floor boards (newb Questions)

Hi All

I have just bought a 1920 semi in drummoyne Sydney. I am a complete renovations newb but was going to try and sand and coat the timber flooring.

I was going to follow the guide here

http://timbercareonline.com.au/diy-sandingstage3.php

http://timbercareonline.com.au/diy-index.php

Is this guide ok? anything else i need to know?

My only question is, Are all floor boards ok to restore? i mean these look like proper timber floor boards, but because i am clueless i am not sure. I mean is there such a thing as floor boards which aren't designed to be "floor boards" but are there as an underlay. If so should i be looking out for something?

Thanks