Hi Mark,
I'm not sure I understand your question, but I'll try to answer it anyway

1. If you buy the software, the limit to use only 50 parts will be lifted. For the rest, the software remains just the same. No missing parts will just appear!
2. If you buy the software, all updates will be free for version 3. With a license for version 3, the upgrade to version 4 will be free as well, including all its updates and patches (this version is not yet planned, so in practice, you'll have at least a year of free updates/upgrades).
3. If you find that parts missing, please let us know, and, if you could, give us the part numbers. We will then try to find the exact geometry, and add them to our release planning. We make no promises here, but normally the parts will be included within one or two version updates.
Don't know if this more or less answers your questions. If not, please let me know!
David.