Certainly possible with the more aerodynamic slugs, at least in a Fosbery gun. Holland's thinking was that the ball and shotgun should be limited to 150yds, although their own testing seem to show accuracy far beyond this range.

This load dropped to subsonic and still proved capable at 300yds.

It also could be Holland's main competitor Westley Richards had a more reliable gun/cartridge for longer range shooting in the rifled choke guns. In taking a stance that 150yds was a limit with paradox type guns they would not have to argue the point of whose system was better at longer ranges.

As to the invisible rifled system, could be it shot as well as the rifled choke guns and if not you would still want your gun to be equipped similar to your competition.
Not first hand experience with the invisible system but reliable hearsay; they don't seem to pattern well. I hope to give one a try someday.