Unfortunately, that kind of depends on the material the bolt is made of relative to the torque. It's always safest to replace fasteners, and you should always do that if the instruction manual tells you to, as that is typically a sign that the fastener is being pushed near its limit. If nothing about that is mentioned, it's a judgement call. If your bolt is grade 5 or A325, the standard chart torque for these is 975 lbs lubricated. Since you are not approaching those values, you could re-use the fastener, as long as the threads look good and there is not evidence of damage to the fastener. If the bolt is a grade 2, then you are torquing it to the max, and you probably should replace it. There is nothing wrong with torquing a fastener to less than the maximum allowable for its grade. Here's a chart for bolt and nut markings
Lock nuts are trickier. If the nut seems to spin on without much resistance, replace it. Typically you can get a few cycles out of a nut without significant degredation of the locking material. In fact, if I remember right, locknuts are often tested for torque retention after five tightening cycles. From your description, the fastener is a nylock, and so is probably good for a few cycles. These do shift the torque somewhat, but you can actually measure the free running torque (the torque it takes to turn the fastener before it bottoms against the joint). This is typically a small percentage of the torque that the fastener is being tightened to, so the change in torque value (or tightening angle) is small and can be ignored. As the free running torque decreases, the amount of preload being applied to the bolt increases.
Since the preload is basically proportional to the amount of rotation when tightening the fastener, you can actually test how much it would change the angle. If you have a small torque wrench and take your time, or better yet a dial type torque wrench, you can measure the free running torque. Once the fastener is snugged up, see how much angle you have to turn it to double that torque value. You will see that this is a very small value.
If you EVER see damage to the fastener, especially stretching in the threads (usually at the thread to shank transition), give the fastener a flotation test. That is, throw it in the nearest deep body of water. If it floats, it might be worth retrieving as a novelty. This test is only to be performed with solid steel objects.
If you are ever in doubt, replace the fastener. It's just not worth the chance of damaging the machine or injuring someone if a fastener fails. If the fasteners are expensive, you can also do some checks by measuring the length of the fastener (and recording it) before installation. You need to be at three decimal place on this measurement, and be careful of how the calipers are registering on the ends of the fasteners. If you re-measure it after use and find it has stretched, you should replace the fastener.
Here's a chart for bolt and nut markings.
http://www.americanfastener.com/technical/grade_markings_steel.asp
If you have any questions about this or want any better explanation, let me know and I'll do what I can. I like teaching people to really understand what goes in to some of the design of their machinery.