Legend has it that the Abt 12 is modeled after Westy 12 and the two compare well. I haven't had both, so I can't comment other than to say that I've seen this written numerous times.
Actually, St Bernardus used to brew the same beer as Westy (same recipes). And contrary to popular belief, St Bernardus is NOT a trappist ale.Found a few tidbits online:
The term "Trappist" is licensed for use by six brewing abbeys. All are Belgian and brew beers under the brand names Chimay, Westmalle, Westvleteren, Achel, Orval and Rochefort. All may use the term "Authentic Trappist Product" on their labelling and most do.
There was a seventh Trappist producer in the Netherlands but its status was withdrawn when its brewing operations were taken over by a large Dutch commercial brewery in 2002.
In 1946, Abt Gerardus makes an arrangement with Evarist Deconinck of the St Bernardus Brewery in Watou to use Westvleteren's recipes. This is the birth of the St Bernardus beers.
The legal restriction in the use of the name Trappist began in 1992. Until that time St Bernardus brewery had been making deliberate imitations of the Westvleteren brews at the request and with the agreement of the abbey, using the St Sixtus brand.