You can use the Drawing Manager to update all drawings at once.
You should also make sure that each drawing has 'Store Drawing in the Project File' checked.
This means that everytime you change applications, ArchiCAD does a quick check telling you the status of your drawing. This doesn't only happen when you switch applications but is also a time dependent action, AC quickchecks the status of drawings approximatly every minute. For external files, quickchecking means that AC is checking the time of change of that file, and this is a very fast process if the file is on a mounted volume.
Cheers,
Link.