VA is not suppose to go on fishing expeditions when an increase or other matter comes to their attention. It can get complicated in some respects.
1. If the rater notices while thumbing through the file an error which has nothing to do with the present situation he or she has a duty to note it.
2. If you filed for an increase in say a heart condition and determined secondary to DMII then they may take another look at the DMII. However, if you have a rating for say a sensitive scar on your left calf then the scar claim will not be looked at because no nexus can be formed between a scar on the calf and the heart.
It's a matter of a claim being linked to another claim and if so then all are open for review.
There is one other way for the RO to review your claims folder even without a claim being filed and that is if you were hospitalized. If you are hospitalized your file is flagged for review automatically by the RO.