This matches the two test strings you provided and captures the firstname:

/^[^, ]+(?:,\s+\w+|)\s+(\w+)/
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Here's my test:

$ perl -wnE '/^[^, ]+(?:,\s+\w+|)\s+(\w+)/; say $1;'
SMITH, A DOE
DOE
BULLOCK JOE A
JOE
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