archive.org keeps copies of websites from as far back as 1996. It was before the 1997 season that USFIRST became FIRST. The
1996,
1997,
1998,
1999,
2000, and
2001 site all refer to the national championship. It is only 2002 and later that FIRST calls it just the championship. But, just like people call it USFIRST sometimes (even though that change happened 6 years ago), people still call it Nationals or National Championship, and probably will for quite some time.