According to the records I can find, the clear band design was introduced towards the end of 1976 for all powder-coated BT lamps irrespective of whatever the coating material was. This was an emergency quality project and by start of 1977 it should have been applied to all types. Even though it was strictly only needed for certain quartz lamps it was applied to all, because it was the same coating machines that produced all lamp types.
In 1979 the phosphor adhesion problems were solved and full coating was resumed. Since that was not an emergency project it seems to have taken longer to introduce, and it was not until 1980 that all types had been converted. The BT56 line seems to have been the last to revert to full coating. If anyone has the time, it could be interesting to make a study of all the Sylvania coated HID lamps on this site from the period eg 1975-1985 to identify which coating design was in use!