What if I don't recompile at all. I will simply install service pack 6.5.5 into the aem instance and my artefact uber jar stays at 6.5.0 itself . I think due to the lesser number of overlays,  there are no issues functionally. But, is the okay to do it this way.

Is it okay to upgrade the AEM with 6.5.5 service pack and keep the artefacts compiled against 6.5.0 itself. We tested functionally and there are no issues. Is there a mandatory requirement that all artefacts on the instance needs to be compiled against the same version.