Sample Size Differences: PUMS v. Full ACS?

I read in the 2020 documentation for the PUMS that the PUMS includes approximately two-thirds of the full ACS sample. Is this the case for all of the 1-year PUMS files (e.g. two-thirds of each year's ACS sample for 2000-2019)? Or do the public use files include a different portion of the full ACS each year?