Deciduous means naked branches in winter, semi-evergreen means half of the leaves are gone and evergreen means the leaves stay on during the dormant season, winter. Most people notice the deciduous because the branches become fully clothed and most people don't notice the evergreen growth because it always was fully clothed. Hope this helps. All plants become dormant in winter.

Here is a link that might be useful: Propagating Perennials

Up north here I don't really think you can truely classify them,as like you say, all the leaves turn to mush.If you are looking to classify a seedling that you want to register,I would suggest a test garden further south to see the foliage habit.

(Raising my hand!!)... Here in Tx, my evergreens stay just that. All through winter they stay green. If there are some warm spells (week +), they will start to grow. Otherwise, they just sit there, sleeping, getting a wee bit tattered from our winds.

Now, SEV is where is gets weird here... I have some that go completely dormant, loose all their leaves (Itty Bitty Blue, Cousin Jewel, Baby Blue Eyes, Desiree, Last Accomplishment). I have some that loose some leaves, and look scrappy (Strawberry Candy, Palladian Pink, Come See, Teardrops in Heaven). And, I have some that look like full clumps (Half Moon Key, Hollywood Lights, Blue Elf, Little Blue Bell, Velvet Eyes, Navy Blues, Hi Ho Silver).

Dormants seem to have varying degrees of dormancy too... For instance, Topguns Pink Lemonade, Miami Heat, Pink Rocks, Party Pinafore are all supposed to be DOR, but they stayed green all through winter. But Catnap Blue, Siloam Baby Talk, Cantique, Tender Love, Changing Latitudes all went to sleep.

I am not sure is this is more confusing or helpful!

Hi ,I do not have to many evergreens do to the fact thay dont do well up here but the ones that make it act like dorments,sev do well .

HI, here in my 6b garden, I observed a lot of variability.
I have all three types, some dormants completely disappeared, while some kept green tips. some sevs. did same, the evs. kept green tips, and some kept a few inches of green. All are growing like champs right now.
Nina