I have upgraded from EE multitenant 12.1.0.2.0 to 18.3.0.0.0DBRU (standalone shiphomes) successful

I have upgraded from EE multitenant 12.1.0.2.0  to 18.3.0.0.0DBRU  (standalone shiphomes on linux) successfully, holding onto all my OLAP objects.  Now I'm downgrading from the 18c3ru directly  back to 12.1.0.2.0, and running into various problems at the catdwgrd.sql  stage.   Is this CDB downgrade path supported?  I have read the doc where it says "yes" and other info where it says you must go back to 12.2.0.1.0 first and then back to 12.1.0.2.0 as a second step.  But  I would have had to plan ahead and do the upgrade that way first, yes?  I would expect that if the upgrade path