I think the Phantom was released in the early '90s.
Brunswick's asymmetric cores haven't been particularly exciting to look at, but they've kept up with most other manufacturers in terms of the mid-diff, at least over the last 5-8 years. When everyone was releasing balls with 0.08-0.013" mid-diffs, so was Brunswick. When most were bumping up to 0.015-0.02", Brunswick was right there. Now that mid-diffs are pushing 0.03" like Morich's EZ Rev core, The Siege is there as well.
Again, they may not be real interesting to look at. The Zone core they used for a few years was dull as dirt but was just as strong asymmetrically as the goofy cores Track was putting into Machines and Rules.
SH