You could do away with the big CASE expression if you use the datename function:

datename(MONTH, ins.lasUpdateDate) + ', ' + datename(YEAR, ins.lastUpdateDate)

As for the actual problem, I assume that ins.LastUpdateDate includes a time portion, why the condition

and ins.lastUpdateDate > Dateadd(year,-1,getdate())

should be

and ins.lastUpdateDate > Dateadd(year,-1, convert(date, getdate()))