HHS first announced the COVID-19 booster shot plan on August 18, 2021. At that point, it had not yet been implemented; it was in the planning stages and was expected to be offered in the fall of 2021.
Before the booster announcement, there was only the requirement for the initial two-shot vaccine regimen for COVID-19 (one-shot for the Johnson & Johnson vaccine). It was only after the initial COVID-19 vaccines were found ineffective that a booster program was announced. Now, there is even a discussion of a second booster, for a total of four shots.
How then did the CDC know from the beginning of the COVID-19 vaccination program to print COVID-19 vaccination cards with four rows to put vaccination data? The card was only for COIVD-19 vaccinations. The COVID-19 vaccinations required a maximum of two shots (Moderna and Pfizer). The cards were printed before there was any publicly known need for boosters. Apparently, the CDC knew from the beginning that the initial two-shot regimen would be ineffective. The picture below was from a February 2, 2021 AARP article.