The first step to deploying a mixed version release to production is to update your resume. You have no reason to believe that in a modern microservice environment that deploying
v2 of service A
v3 of service B is going to work when in all lower environments it is v3
Real companies do this by having fancy canary deployments, rollbacks, deploy code from dev to prod daily, etc.
If your deployment cycle is 12 months, yeah, update that resume before deployment.