It’s been our mantra for more than two years now: A lower exchange rate will drive a rebound in non-energy exports. But evidence of this development is still sorely lacking at the industry level.

Of course, as we wrote last week, we did see a huge jump in exports in June. Despite the glimmer of hope those results offered, one month does not a trend make (that’s another mantra).

From the perspective of a U.S. investor, these concerns may seem entirely academic. After all, the tailwind we once enjoyed from the rising Canadian dollar has since turned into a significant drag on investment performance now that the exchange rate is sharply lower.

But while the stock market and the economy don’t always march in lockstep, a resurgent economy will help drive growth in our stocks. And a rebound in non-energy exports is one way to get there, at least according the Bank of Canada (BoC).

The central bank believes strong exports will drive business investment, followed by hiring, wage growth and consumer demand, leading to a virtuous cycle of economic growth.

Right now, the BoC’s wish list might seem like a relic from the period preceding crude oil’s collapse. But with the expectation among some economists that energy prices will be lower for longer, finding new growth in the non-energy sectors has become even more urgent.

Unfortunately, as the central bank has famously observed, the relationship between exports and a lower exchange rate is no longer as strong as it was in the past. More recently, the central bank even conceded that it was “puzzled” by the weakness in non-energy exports that prevailed prior to the June surge, as only so much could be explained by bad weather coupled with the commodities crash.

However, CIBC economists have one plausible explanation: The lower exchange rate needs more time to work its magic. The bank notes that it typically takes six quarters before the depreciation of the currency fully translates into gains in exports.

While it’s true that the Canadian dollar’s decline began gathering momentum in mid-2013, CIBC says that by historical standards it was still trading at a relatively expensive level through mid-2014. It wasn’t until late last year, as crashing crude drove the Canadian dollar lower, that the exchange rate finally reached a level that should be beneficial to trade.

With only six months of trade data since then, that means, as CIBC puts it, that the lion’s share of the benefits of a lower exchange rate have yet to be revealed.

At the same time, it’s possible that the lower loonie won’t have quite the same effect on exports as it has had in the past. CIBC notes that a 20% depreciation in the exchange rate has historically boosted export volumes by 12%. But that might not be the case this time around.

Part of the problem is that while the once-strong Canadian dollar was enhancing our investment returns, it was also eroding Canada’s manufacturing base, causing it to lose significant market share to countries such as Mexico.

And that was after the manufacturing sector had already suffered a devastating blow from the Global Financial Crisis.

The relatively high exchange rate that prevailed during much of the ensuing recovery means that the sector has recovered little of the capacity it lost during the downturn.

Now that some of the key conditions are in manufacturers’ favor again, they can’t exactly ramp up production without the factories that have been shuttered.

The good news is that CIBC believes the exchange rate is already at the level necessary to spur growth for export-oriented manufacturers. The bad news is that they believe it will have to remain at this level for at least a couple of years to kick-start the sector again.