So you doing periodic as a safety check and issu satisfactory certificate cause it complies with 15th edition and it is safe while 17th edition released so far. Something goes wrong and the reason of that would be one of the reasons why they amended 15th edition up to 17th and will come back to you saying you said it is safe. So what excuse you will say? I made a note that it complies with 15th edition put my signature that it is safe and you let landlord to get away for 5 years without upgrading installation to current standard which is safe enough for nowadays. I think note is not good enough because people do not understand 15th or 17th ed they only want to get clean and satisfactory cert. All techs moving and they have to maintain and upgrade their electrics as we do maintain our cars etc. It's like I said probably better to write that installation in good order but needs bringing up to standard rather to issue satisfactory.
People that decide that an installation is unsatisfactory just because it doesn't comply to the 17th IMO are incorrect. Most times it is scaremongering to get some remidial works.