Bitcoin Core often backports fixes for bugs and soft fork activations into previous software releases.
Generally maintainers will handle backporting for you, unless for some reason the process will be too difficult. If this point is reached a decision will be made on whether the backport is abandoned, or a specific (new) fix is created for the older software version.
An overview of the software life-cycle for Bitcoin Core can be found at https://bitcoincore.org/en/lifecycle/