Evergreen, Deciduous, Semi-deciduous Orchids

[TheOrchidHut]

When it comes to these botanical terms for orchids, it seems that evergreen and deciduous are clear. However, how would a semi-deciduous orchid loose its leaves? Some schools of thought seem to promote leaf loss specifically every two years in order to meet the semi-deciduous definition. Other interpretations seem to support any sympodial orchid that looses older leaves on back bulbs/canes as semi-deciduous as well, regardless of the time it takes to do so.

Any input is appreciated - the debate seems to be never-ending.

Thanks!
-D.