audit: purchase cut off testing

我需要做purchase cut off test
before after yr end 各十單

但係入ledger date同purchase inv date唔同
(d purchase係海外買返黎)
所以唔多知邊十單先係最尾十單
我洗唔洗ensure一定係尾十張(by purchase inv date)?
點解決

after yr end頭十單
我睇purchase voucher裡頭
頭幾單invoice係dated before yr end 但係過左yr end先收貨
所以又唔知係咪一定要將呢d items揀晒黎test先
先至再test其他 (invoice dated after yr end)?
p.s.
1. 有d invoice/shipping無夾0係purchase ledger 得收貨單
2. 雖然做stocktake同埋stocktake report既時候已經obtain左yr end 最前最後既invoice(但當時盤數未完成)

plz help