Your definition of theory only fits if you scope it so narrow that it's useless to the problem space.... Because the point is that theory didn't entirely cover that space. And bridges did collapse because of that.
But lack of theory didn't mean lack of rigorous testing. Gergie was built based on theory. Many other bridges were based on testresults..and did fine.
>Many other bridges were based on test results
I'm going to go out on a limb a little and assert that not a single bridge was built out of steel or iron in the last 200 years in the US or the UK without a static analysis of the compressive and tensile forces on all the members or (in the case of bridges with many hundreds of small members) at least the dozen largest members or assemblies.
It should be obvious that when you talk about theory covering a product, there either is a theoretical framework, or there isn't.
In the case of suspension bridges there wasn't. There was no mathematical theory to explain how the bridge stayed aloft, or how much it could carry.
What bridge builders of high quality did, was make mock (small) models. And test how much rocks they could put on them.
I think you will concede that that isn't a theoretical model. It's a practical one.
And this happens very often. People experiment and build useful things, but no one understands why they work. Until later people come along and explain the phenomenon.
That's not true, even for the first suspension bridge ever built (in the early 1800s), but it is true for example that many useful and impressive aircraft were built before the development of a physical theory of flight.