I had this discussion with my NICEIC assessor very recently.
In the past, with ELECSA, most years I presented a consumer unit change, and that was always sufficent. Now (sadly) merged into NICEIC, I noticed that was no longer enough, and in fact ditched the job I'd planned to use, and found another job that also included some new circuits. But mostly what I like and do in the way of notifiable work is consumer unit changes.
Explaining this to my assessor, he said he'd be happy with just an extra small circuit, and more or less said you can always install a new socket under the consumer unit! Whether this is enough I expect comes down to the individual assessor, and I'd not risk it, so I'm going to make sure I have a job with a decent new circuit or two, even if it means installing something for free for a customer, to be able to use the job.