You can't recover the database to any point in time or SCN that is on or after the beginning of the missing archivelog. Oracle cannot and does not allow you to skip a missing archivelog.
Thus, if the archivelog Sequence#1020 was for transactions from 10:01:01am to 10:48:42am of 25-Aug and is the missing archivelog, you can recover the database only upto 10:01:01am even if you have Sequence#1021 and subsequent archivelogs available.
Note that if you have a database backup that began after 10:48:42am, you can use the more recent backup to ignore the missing Sequence#1020.
Hemant K Chitale