I've used my cheap torque wrenches in a pinch the way you have and they survived. Although, I never exceeded the limits of the wrench. Assuming this is a clicker type, they operate with a spring. If you went too much over the limit it could have caused some damage.
Checking the torque on an already tightened bolt with another torque wrench is okay if you're only trying to be accurate within 5% or so. If you're doing a bunch of TTY stuff I'd be really cautious until you can at least verify it on a tool truck. Keep it with you and catch one at a stop, they're always looking for more customers anyway. Just a forewarning, you might walk off with one of these . Those trucks are dangerous!
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Nothing like a few thousand sitting in the top drawer.