"So you believe that the taxpayer now filing independently in 2020 will get a credit of $700? ($1200 minus the $500 the parents got for the dependent taxpayer in 2019.)"

Sorry, no. I now see you asked Two Parts. An individual tax payer will fill in the tax return and submit the info for that filing status, which means a $1,200 credit for that individual.

As for rebates, collections and differences, it's still a bit of a moving target.

Keep in mind some stimulus checks were reduced by tax debt.