Your history is a little spotty on data and details, after so many years, so I expect there are lots of questions I could ask for which the answers would not be easily accessible. I can say, though, that my experience with NVLD is that quite a lot of individuals have early delays in phonetic reading or spelling (so their early identified disability is often dyslexia or dysgraphia), but that once they reach reading fluency (by whatever means works--some use whole word reading, instead of phonetic decoding), reading can really take off, leaving deficits in math and other visually-related skills to reveal themselves (so that, in some cases, the disability area actually changes to mathematics by secondary school). And many compensated dyslexics (another name for stealth dyslexics, that probably better describes situations like yours) can read without apparent difficulty, but still can't spell without excessive effort. A simpler description would be to leave it at dysgraphic and NVLD, which covers everything you've listed.
The shorter vs longer text phenomenon may be because you probably read (decode) more from context than you realize, so more context (longer passage) makes it easier to read and comprehend. If you have challenges in visualizing the meaning of the text, having more text to work with also may help you create a picture more easily. Also, word problems are math.
