Because there are some configuration differences between firmware versions, you have to be prepared for the changes. As you are upgrading through a large number of firmware upgrades, you will need to read a lot of release notes.
On the whole, I have never had much problem upgrading Procurve firmware, but then I generally upgrade them reasonably frequently. I used to read every release note when it was issued to check what was fixed and what was added, and I tended to get an upgrade in at least once a year, sometimes more often.
