I believe the theories being offered about absolute airflow and it's effect on jetting at various rpm range is based on false premise.
The vents present in these carburettor (any carburettor, in reality) feeding the float chamber, don't contribute to the air supply consumption of the engine.
Effectively, the "main" route through float bowl standpipe is to supply method of maintaining atmospheric pressure conditions inside the bowl. Secondary function to act as weir type overflow should the feed valve become impaired. The long tail pipe is really a courtesy to avoid spilling fuel onto the engine in this eventually, also to alert you easily via the puddle it make on the ground, to the failure of the carburettor float valve.
Its not a constant flow of air through and into the chamber. It goes back and forth in very small amounts based on system response in filling the chamber with fuel .... this to specifically avoid a pressure shift and hence disturb the overall jetting balance.
ALL fuel total consumed by exit through the jet is immediately replaced by exact volume of fuel coming in from fuel tank, else the notionally set float height would vary too much. The vent just allows free flow of this action. It's not a supply route in itself.
Should there be a failure in blocking or impeeding this function, then the carburettor COULD pull vacuum on that overflow pipe. The auxiliary vent should prevent that eventuality by providing a leak, as such. There's also no filtration fitted to these tubes, making it potentially problematic to "syphon" through any of them.
Like the Honda second/return throttle cable, like separate brake circuit on vehicles, they'd not often be called into use .... but they are fitted anyway. It's a responsibility in production design to cover unseen events in normal use.
The two vents should not exit at the same place if its to avoid a syphon risk. Neither should any of them be subject to pressure (positive or negative) as that would influence float bowl neutrality in parity with ambient atmospheric ... ultimately to influence jetting against manifold depression, which would shift mixture uncontrollably.
