Well this is a topic that would certainly be interesting to hear some discussion on.
In both of my 83's it is definately a coolant recovery system. When the engine is hot and the coolant expands it overflows into the tank and as the engine cools off after stopping, the overflow is sucked back into the radiator. I have marked the level of the coolant cold, then marked it hot and monitored it coming back to the level of cool.
At least to me, that makes is a recovery system not just a collection tank.
Now if you are missing the little tube that runs from the cap to the bottom of the tank, then your system would only act as a collector as there would be no vacuum established to suck the fluid back into the radiator. Same thing if you have an cracks or holes in the tank. I have had problems when that little tube got clogged up with gunk, but once I took it apart and cleaned it out, it started functioning properly again.
I vote it is designed to be and functions quite well as a coolant recovery system. As long as the coolant system is sealed and functioning properly.
I keep getting connection refused or page cannot be displayed. Where can I get a copy of this magazine in the US? I looked at barne&noble about a week ago and they have several british car magazines but not this one.