Yes, there were certainly girls named
Brianna before 1970. The US Social Security department provides records of all names which have been used at least 5 times in the US, for every year since 1880. (You can access this at
https://www.ssa.gov/OACT/babynames/limits.html).
This data reveals that 31 girls were named
Brianna in 1970, 19 in 1969, and so forth. The first year in which
Brianna appears is 1963, when there were 8. This does not mean that there were no girls at all named
Brianna before 1963, but if there were fewer than five in any given year, they would not be included in the data.
For instance, although this is not the same spelling, I had a high school teacher named
Bryana, pronounced like
Brianna, in the 1980s. Since she had a daughter my age, she could not have been born later than about 1950. So the name, in various spellings, may have existed at a low level for quite a long time.
This message was edited 4/30/2020, 8:07 AM