The year goes by Jan 1 - Dec 31. If you are doing a 2019 return you report all your income for 2019. Wages for 2019 and Social Security. Don't get confused by the year when you file it like in April of the next year. Like a 2019 return is filed in April 2020. This year in 2023 we filed our 2022 returns for the year ending 12/31/2022.
You need a W2 that says 2019 on it, not a 2018 W2. 2018 income should have been filed in April 2019, but it is still a 2018 tax return. You enter a 2019 SSA-1099 on your 2019 return.
Hope that doesn't confuse you more. Don't worry about what year it is filed.
