In response to David's post I have checked on the state of Brindled beauty in Ceredigion. There were just 24 records before 2000 but there has been 163 records since 2000. The following distribution map shows that the records are spread around the county.
It is true that more people have been recording moths since 2000 but I think the graph indicates increasing abundance of Brindled beauty in the county. The moth is described as frequent to abundant in southern and eastern England, and that it has been spreading away from there, with greatly increased numbers in Yorkshire. Its range appears to have increased in Wales too.
In Butterfly Conservation's "The State of Britain's Larger moths 2013" Brindled beauty was reported as having declined by 87% in the 40 years up to 2007.