IIRC the C-64 was announced on January 7, 1982 at Winter CES, but didn't actually go on sale until August 1982, and didn't become successful until 1983. But yes, the C-64 was feature-complete by January 1982 so I guess January 7th was its 40th birthday. Happy birthday!

January 1982 was just a year into the VIC-20's lifespan, so as far as Commodore's business that year, the focus was still firmly on the VIC-20 (which peaked in 1982, and was made until January 1985) and even the last-generation PET models, which were in their last year of production. The early production C-64's had some design flaws that I think were solved by 1983. With the PET gone and the C-64's price dropped to $300, the computer really took off that year.

My dad (born in 1968) had a C-64 as a teen himself. Now he's a computer programmer.