account--Purchases invoice

如果題目有一句寫The total of a purchases invoice was undercast.

我想問，佢purchase invoice undercast的意思係
1.)只係張invoice undercast;
2.)張invoice undercast之餘，purchase day book最後個數都undercast;
3.)張invoice undercast之餘，purchase day book最後個數都undercast，creditor個數都undercast.

purchase invoice undercast/overcast點解唔會影響agreement of trial balance?請解釋。

唔該~