Fertility Data cdc vs acs

I have noticed a big discrepancy( which only increased post covid) in the fertility rate and births reported when compraring the ACS data with the CDC data, 3.6M births in cdc and 4M in the acs for 2023 for example.

Why is the difference so big? It certainly cannot be justified solely based on the acs being for the mid point of the year and so for births for 2022M7 to 2023M6. Even adjusting for the possibility of some women who had a birth in the last 12M having had the baby outside the US the difference is still too big

1. Will this discrepancy eventually be solved? Was hoping to get fertility data by language spoken but with differences of over 10% it gets difficult getting reliable data.

Thanks in advance