Rule reminder
'Purché', 'a patto che', 'a condizione che' = 'provided that / as long as / on condition that'. They always take the subjunctive. With a past conditional main clause, use pluperfect subjunctive. With a present or future main clause, use present or present perfect subjunctive depending on whether the condition is simultaneous or already completed.
Il consiglio avrebbe approvato il bilancio, purché i revisori … (certificare) i conti senza riserve.