This is a working version of the link.
The gist of it is that rooting powder is practically useless, I have always used it but haven't any way of telling whether it works - I have put my failures down to poor technique!
There are two main rooting compounds, indole-3-butyric acid (IBA) and 1-naphthaleneacetic acid (NAA). You can buy only NAA in garden centres, usually in powder form but sometimes as a gel. IBA is preferred by commercial growers and harder to get hold of- I have bought some on-line - think it came from the USA - was it called Clonex??
I am no expert by any means, and am ready to be contradicted, but from what i understand, the shelf life for NAA in powder form is around four years. It often contains a fungicide and this element may have a shorter life span. I think that the liqquid version of NAA is a lot less - a year or so, but am not sure as to why.
I understand that IBA has a shelf life when dry of three years, but is usually applied wet, either in alcohol or water, and like NAA, in this form its shelf life is a lot lower.