If the cable is as stiff as old boots and difficult to "form" - it springs back to near straight - then it's A5, which is an inert insulation with 19 thickish strands. The A4 cable is seemingly a classic 42 strand with a web "spacer" between the conductors. In our situation, the black A4 aged over a few years and all the internal copper went dirty looking. The white A4 was better in this respect.
The A5 is silly money now, but does work well with softer sounding valve amps. It was magical with my Quad II's as I remember and IMO only really worked with Olive Naim over very long runs (several metres each).
P.S. The A4 had the Naim logo and text stamped into the webbing IIRC..
Tear down these walls; Cut the ties that held me
Crying out at the top of my voice; Tell me now if you can hear me