Any number of design factors may have resulted in your current configuration, such as:
1. Safety Factors.
2. Mitigating Factors.
3. Operators assuming "If it fits, it'll work. Add the new pipe(s)."
4. Historical emergency events.
5. Properties changing over time (e.g. that acid plant that's known the spring minor leaks every so often).
In general, every time a pipe is added to a structure, it should be checked. For small diameter lines, at least a cursory check should be performed, including an inspection.
In general, after a major emergency, as well.
In general, whenever you inspect a pipe, you're also inspecting the supports. If a line is in cyclic service, so are the supports. Therefore, they should all be tied together.