Groundcover berries - how many years to fruiting?

Not knowing specifically about permaculture in past years, but leaning toward a concept of edible landscape, I have stuffed my tiny city lot with loads of edible shrubs, trees and perennials. Have had many successes, especially considering my coastal Oregon location. However there are a couple groundcover berry plants that have been in the ground 3+ years that have yet to show even a single berry: one is lingonberry, the other a spreading cranberry (variety Stevens). Both are growing well and appear healthy, with good annual shoot production and the lingonberries (2 plants) definitely flower, but no fruit. I have yet to see the cranberries (3 plants) flower or fruit.

Observing the many similar plants that flower and fruit in my landscape, I cannot figure out why these are not producing and wonder if others have experience with them. Climate should be adequate, soil acidity & fertility, exposure, supposedly self-fertile. So are they just too young? Does it take several years? I would like to know as I am a professional landscape gardener and like to "sneak in" edibles to my clients' landscapes -- edible evergreen groundcovers are especially valuable.

It may be they are just young, but if the bush is flowering that seems unlikely. My suspicion is that they may need a different variety to cross pollinate. Even fruit that is 'self fertile' will apparently frut better if ithas a partner.