The register continued in use by the NHS until 1991. Notes relating to an individual shown in the register were added on the right hand page, following on from the original entry. We are not able to see the right-hand pages, but if the space for notes relating to an individual entry became full, it was common to enter the individuals details again at the back of the enumeration book or in a continuation book, where the line on the right-hand page could be used for further notes relating to them. The original entry would be marked "See page nn" as you have found.
Depending where you are viewing the original page image, you should be able to browse through the images of further pages in the book until you find page 12.
Again, you won't be able to see the additional notes created for the individual on the right-hand page. The entry that you can see will in all likelihood just be a copy of the details you have found on the original left-hand page.