No, that’s wrong.

The “less than” vs “fewer than” rule isn’t about whether you know the exact number - it’s about countable vs uncountable nouns.

Video game copies are countable, so it’s traditionally “fewer than 1,000 units” regardless of whether you know the precise number sold.

That said, it’s been misused so much that it’s become more flexible, and “less than” with numbers is widely accepted now.

Don’t take my word for it, Google it.