When I worked for a big enterprise company writing simulation software, we did quarterly or bi-yearly releases, but the defense clients wanted to run their own

When I worked for a big enterprise company writing simulation software, we did quarterly or bi-yearly releases, but the defense clients wanted to run their own verification and validation tests generally, so they maybe upgraded once every 2 or 3 years. When I went to work at a University as a research software engineer, a particularly memorable incident was a research group getting very angry that we were upgrading the cluster to CentOS 7 thus meaning the ancient version of COMSOL they were contractually obliged to use in a contract with Rolls Royce would no longer run at all. We ended up getting something working using Singularity but it was very painful.