FDA regularly issues what they call "uniform compliance dates" for regulations finalized during certain time periods. Typically when final rules are actually issued, they have a compliance date built in so the uniform compliance date is just a general guideline. The final rule for the changes to the nutrition panel were issued in 2016 so this uniform compliance date does not apply to those requirements.
The compliance date for the changes to the nutrition panel for large companies was January 1, 2020 and for smaller companies was January 1, 2021. However, FDA has stated that they were and are exercising their enforcement discretion for compliance with these requirements. The excerpt below is from their website.
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I understand that FDA has received multiple requests from manufacturers to provide additional time to comply with the new requirements. When do I have to meet the new requirements?
The FDA heard from several manufacturers and industry groups that more time may be needed to meet all of the Nutrition and Supplement Facts label requirements. Manufacturers with $10 million or more in annual food sales had until January 1, 2020, to meet the requirements, and manufacturers with less than $10 million in annual food sales have a compliance date of January 1, 2021.
The compliance dates are still in place, but the FDA intends to work cooperatively with manufacturers and will not focus on enforcement actions during 2020 for larger manufacturers and during 2021 for smaller manufacturers. This additional flexibility includes manufacturers of single-ingredient packages and containers of single-ingredient sugars, regardless of the size of the manufacturer.