Ok, I'll start this off by saying I don't know. For many years I've used a clicker type torque wrench. Probably a lot more than most people. If there was a torque spec, I used that wrench. And a number of mechanics have told me that within a few months of buying one, they go out of adjustment. But, again, I would make a large bet that they are either voicing their belief or guess. Perhaps it was based on their experience with maybe one or two t-wrenches, but certainly not based on a decent sampling of wrenches tested carefully over a period of months and years. I've read precious few long term tests of tools or anything, for that matter, that gave useful information on durability and accuracy.
I thought of building a jig - a shaft held by two ball bearing pillow blocks with an arm welded perpendicular to the shaft 1' long, and a nut welded to the end of the shaft. With the shaft turned so the arm was horizontal, and by hanging a weight from the end of the arm, I could put the torque wrench on the nut and see if it clicked when, say, a 20 lb weight (20 foot lbs) was just lifted by the wrench. I never did. And I know nobody who has practical experience calibrating torque wrenches - someone who can say which ones hold their accuracy best.
Consider this. The beam type with a pointer moving over a scale is very very simple. Its accuracy depends on the characteristics of the metal shaft (and not being dropped). You cannot read the scale to more than maybe + or - a few foot lbs. The click type is also pretty simple. Having taken one apart, the mechanism depends on a spring inside. And we know that springs can lose tension over time. If this type is well designed and in use the spring is kept well within its tolerances, it too should hold accuracy for quite a while. Note my use of the word should. I'm guessing (ruminating, actually). What these devices do in the real world is another story. Finally, the dial type has to have some kind of rack and pinion or wire pulling on a lever mechanism. This is going to be more complicated than the first two types, and is probably more subject to damage from drops or hard use.
Today they make (expensive electronic) torque wrenches with small strain gages glued to the steel beam. Scales are made with these gages, and are pretty accurate and durable, but don't forget that scales are tested and certified regularly. In the real world, we wrench on our bikes in all sorts of positions, and dials and gages are often not easily watched from a vantage point perpendicular to the gage (for accuracy in reading it). For my money, I prefer the clicker type. I have 3 of these and one beam/pointer type. And, I confess that I close my eyes and believe they are doing what they are supposed to do, and are doing so correctly.