Yep, that's the idea.
PSA here: BE SAFE.
That being said, It's important to note that they probably aren't tip toeing the line in safety. They wouldn't rate the can for 12 in for 308 if a very mild load would turn the can into a grenade at 11.9 in. You can probably get away with more than what they rate it for but if you do damage the can it would be kind of inappropriate to ask them to honor their warranty.
So in your case, I'd imagine you could get away with mild 308 loads in a 14.5 in barrel. They are essentially saying with their ratings that if you put a hot load in a less than 16 in barrel, you just might permanently damage the can. If you don't do that, you're probably safe.
One thing to remember though, barrel pressure isn't linear so half the length isn't twice the pressure. It's more.
Here is a random example.
All that is to say that putting an Omega on a 14.5 308 probably won't turn it into a grenade but if you happen to run some hot loads I might be a little concerned that the baffles would deform, the welds would weaken/break, or you might get a slight tube bulge.