Playing as Prussia, an unaltered installation. But to check it I also started a game as Austria: the same problem prevails.
Elements of garrison and fortress units, including Coastal Artillery (maybe all units which are immobile/fixed ?)
are not included in the Replacement Pool, and thus cannot receive replacements.
Here what you can see from the start, no icons for fortress and garrison elements, no chance to replenish them:
[ATTACH]39992[/ATTACH]
And here the result after having played one and a half year. All these units are doomed, after 10 years without reinforcements, they will be no more:
[ATTACH]39994[/ATTACH]
[ATTACH]39995[/ATTACH][ATTACH]39993[/ATTACH]