AP did a special version of the Avanti for Y2K and called it the Century. They installed the SEAS tweeter from their then $20k Caldera and modified the crossover to better mate with the Avanti's custom midrange driver made from cast magnesium. A second crossover update was done a few months later to the Century which gave another 4db on the low end, bringing its response down to 28Hz. To my knowledge there was never a second instance or newer speaker from AP with 'Century' in its name.
I think the Libra was a fine speaker and I enjoyed auditioning it - a bit more laid back and not quite as quick as the Avanti Century, but not a sufficient increment better than the Virgo to succeed financially. Put differently, at the time, AP had too many price points too close together.
I have not heard a Virgo III, but, imo, the Century easily dispatches the Virgo II - as nice a speaker is the Virgo II, frankly there is no comparison. The Century never gave a sense of image miniaturization as the Virgos sometimes did. Bass is tauter than the Virgo, and while it won't plumb the lowest lows, the Century's bass yields v. nice pitch with a tonal 'rightness' to it. Excellent sense of air up top, and easily capable of conveying the spaciousness of a concert hall. The Century does so many things very well and it will reward top-notch cabling and upstream electronics.
I'll give Narrod a bit of pushback on his claim about the Century's ability to dissappear into the soundstage - quite the contrary. When dialed-in properly in an AP nearfield arrangement, the Centuries present a full orchestra entirely behind themselves within an incredibly deep soundstage. Dividends come from time spent to get the set-up 'just so'. Soundstage width will be a function of relative distance to the sidewalls. If electronics or recording production values bring an instrument forward, the Century's won't hide this, while they are superb on well recorded orchestral music.
Fwiw, the lineage goes: Avanti, Avanti II, Avanti Century, Avanti III ... The III was the last Avanti designed by Joachim Gerhard.