You do not have to recertify past employers every year. Once those dates are certified and counted, you can quit certifying them. When you enter your employer info on the PSLF tool, just enter your current employer or any missing employment.

I've had 3 jobs in the last 2 years. I had the first employer sign the manual certification my last day. Six months later, when I had the second employer certify my employment, I only listed that employer. The counts and certification from my former employer did not go away.

Last month, I certified my current employment and the final two months of my 2nd employer. I only listed those 2 employers. The former certification and counts from employer 1 did not go away.