Evidence of fact: new evidence
If new evidence of facts (i.e. evidence previously unknown to HMRC) comes to your knowledge you may make further assessments in respect of the same period whether or not that period was reviewed on a previous visit.
It follows therefore that where a number of separate lines of enquiry are being followed and further information is needed, each one when completed may lead to a separate assessment for the same period. The one-year rule runs in each case from the date that HMRC receives the appropriate information, which may or may not be the date of the visit.