My curiousity is piqued, I will have to check.
There are firearms made pre '98 and post '97. The FRT tends to classify these as if they are all modern, so the FRT listing may not be an absolute. It becomes necessary to establish that the particular revolver was actually made pre '98. This can be difficult.
The H&A XL Bull Dog is listed as a prohib, because of calibre or barrel length.
The company went through a number of reorganizations. In 1898, Hopkins & Allen became Hopkins & Allen Arms Co. I do not know if the version of the company name would be recognized as evidence of period of manufacture. If there is evidence that the company marking on its products changed with this reorganization, it might be possible to establish antique status.