Believe chime springs have been over wound
The idea of "overwinding" is probably the most common myth in clockmaking. A clock cannot be wound too tight, unless it is wound so hard that the mainspring breaks, in which case the spring becomes completely unwound and will not wind up again. What has actually happened is that the clock is fully wound, but does not unwind because it is not running for some other reason. Letting down the mainspring would have no benefit.
You're correct that the clock was made in 1974. This is far beyond the expected lifespan of the clock. It is possible that lubrication by a qualified clock repairer could get the clock running again, but considering its age, it may be more likely that the movement is worn out, dirty or corroded and needs replacement.
The three keys should be wound all the way, as far as they will go, once a week. This clock should be self-starting when wound, so the fact that it has been sitting wound without running for years indicates a previous problem that prevented the clock from starting and running the mainspring down on its own.
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