I would check the download link for your previous purchase and see how much you paid at that time, what I've noticed is you only get access to downloads that cost what you paid before or less... so if you bought a version on sale for $5 (like I did) you will not be able to download this new version that currently costs $10, until a time it also costs what you paid before.
Viewing post in Knightly Passions [1.03 version] 18+ comments
it doesn't add together... it just looks at what the highest amount you paid at once and compares that to the prices of the available downloads. I don't know if folks set sales and prices intentionally to manipulate this behavior, but it does make buying something on sale that isn't finished a bit unappealing since it likely means you'll have to buy an updated version later if it isn't ALSO on sale.