Radiator coolant was never filled "full to the bottom of the cap" or it would push the coolant out the overflow. Typically, "FULL" is any amount over the top of the tubes seen in the radiator core, often as much as half full of the upper tank but usually less than the upper tank being 1/2 full by my observations (to not ever see coolant loss out the overfow).
Original radiator caps were never designed to accommodate the coolant recovery system. Coolant Recovery systems became prominent during the 70's, it was discovered that the oxygen going in and out of the radiator vent tube (overflow tube) was causing premature corrosion and degradation of the coolant itself. Many owners bought conversion kits in later years because of this then, "new design".
On daily driven examples, it is still a good upgrade, just like shoulder belts, power disc brakes, collapsible steering columns and the likes of safety/convenience upgrades but NONE of these are original equipment and thus a topic for another forum or discussed at this forum in the Lounge.