You can update a pending translation only if a translation is already in progress for the target language on the map or topic you select.
The first time you submit items for translation, Astoria holds off importing the documents until all of them have been translated. So even if individual documents are marked Complete, Astoria doesn't import them until they are all Complete. Once the translator marks the job as Processed, Astoria imports all of the items and then marks them as Delivered in GLE TMS.
When you submit a translation update for pending items in a translation, if the items have already been marked Complete, but they are resubmitted for update, when the translator marks the updated items Complete, Astoria imports the translated items as soon as it sees them.