diameter 1.6mm
radius 0.8mm
cross sectional area of strand πr²
3.14159 x 0.8 x 0.8 = 2.01 sq.mm.
2.01 x 7 = 14.074 sq.mm.
It means your measurement is not quite right - or the cable is between 10 sq.mm. and 16 sq.mm.
Why have you changed your mind?
Well, yes they should be unless someone has done something stupid.
Yes.
Cables are very corroded. Strip them back until the wires are shiny copper.
The CPC(earth wire) should be connected at the other end.
The yellow wire should also be terminated safely at the other end - or it could be doubled-up with the red or blue wire.