Found this out the hard way this afternoon after my VSO gave me a heart attack. Make sure when you file supplemental claims, you either grab all the paperwork from the original claim and include it, or call and work with the VA to get it dragged forward.
Long story short, VSO saw a denial letter for my claim. Claim is actually pretty strong (was missing a nexus, had the flight doc that treated me write one). Waived the new exam because wasn’t going to roll the dice with a shitty CP exam. Come to find out the denial was for a lack of DBQs. Luckily a senior rater caught it in step 7 and kicked it back, but save yourself the stress earlier and just file everything you have with supplemental, because apparently raters don’t dive back into the initial claim to look at that information, just what’s in front of them. Idk if this is common knowledge, but it sure took me by surprise to say the least.