Having now re read the WR it does state that the periodic notice shall be applied following work completed in accordance with chapters 61 and 62 i.e. initial verification and periodic inspection.
In the OSG it states that the notice should be completed on the initial verification and updated on each periodic inspection.
If we were to apply the WR wording with the meaning of initial verification being the inspection and testing of any electrical work including additions and alterations then this would mean that any change made to the electrical installation that would require an installation certificate would require the notice updating.
However I would refute this on the grounds of absolute stupidity on the part of the IET.
I believe it should mean only the first initial verification of a new installation and any EICR.
If I move a light fitting and provide a minor works certificate (i.e. initial verification) then I should complete or update the periodic inspection notice, however I have insufficient knowledge of the entire installation to be able to provide a meaningful retest date therefore it would be inappropriate to make any written claim to this effect.
If the work you have done is sufficient to provide a meaningful assessment of the installation then it may be sensible to update the notice.