I don't know if I understand you question yet - sorry. I believe I was answering your question, but maybe not.
If you have FormTemplate v1.0 and create Form A from it, and then you upgrade FormTemplate to v1.5, there is a default upgrade.xsl that will make sure that Form A is compatible with the schema changes when you open it in v1.5.
If upgrade.xsl doesn't exist or doesn't do the job you need, there is a way to write you own upgrade.xsl or do the upgrade via code.
Greg Collins [InfoPath MVP]
InfoPath Dev