Machado, 56, had led her rivals by some 40 points in polls.
Though five people were released, the Maduro government said last week that those with disqualifications cannot run in the 2024 contest.
The opposition, which says the disqualifications are unlawful, has been reticent about what it would do if Machado wins the primary but is unable to compete in 2024.
Machado has said she could pressure the electoral authorities to let her register, while others have argued a substitute will be necessary.
Reporting by Vivian Sequera and Mayela Armas; Writing by Julia Symmes Cobb; Editing by Tom HogueOur Standards: The Thomson Reuters Trust Principles.
Persons:
Maria Corina Machado, Nicolas Maduro, Machado, Carlos Prosperi, Maduro, Vivian Sequera, Mayela Armas, Julia Symmes Cobb, Tom Hogue
Organizations:
Venezuelan, Thomson
Locations:
Caracas, CARACAS, United States, Machado's