Slitherine

I was testing a fairly large in scope, multiplayer map based on the Ost front north of the pripyat marshes. On turn 15 or so I realized I should have new units available to purchase or upgrade to.

So, I just made a little test map. Placed a tank and a AT weapon down.
Scenario Params Turn duration is set to 8760 hours (or 1 turn = 1 year)
Set test to 5 turns...click click click click...
To my surprise no new units became available to purchase or upgrade to.
I know each unit has a historical availability value attached to them.

I understand the unit availability dates work at the start of the missions, but I need it to work DURING the mission as time moves forward. Is this even possible? thanks.

I'm also looking for a solution. I want to build a scenario from 1941 - 1945 in which the historical units become available in the purchase menu.