I personally would prefer running in another bond, but if that is not an option then joining is fine.
I would not even consider running a new protective bond in unless it was feasible to do so. What I mean by this is that if it required a lot of time and effort and caused major disruption within the property then I would not think twice about connecting to an existing local service bond. This may be by lugging onto the BS951 clamp or through crimping to achieve the desired amount of cable to reach the new bonding point.
When carrying out an EICR I would not comment or assign a code to this as there is no breach of any regulation. We are not expected to use and comment about any of the guidance notes when carrying out EICR's. However, we are required to use BS7671 and access and make a judgement on compliance.

