Russ,
Like Don, I would be on your a$$ like a blood-suckin' tick!
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Of course, like most folks, I would be very hard pressed to determine if you actually missed a passing chord.
As for the singing, some folks can, and some cannot. For those that cannot, I encourage them to take vocal lessons, which can be extremely helpful for a large number of individuals with marginal singing abilities. Many of those that have taken my advice and enrolled in community college vocal courses have really blossomed into wonderful singers. I guess what I'm trying to say is I would use diplomacy.
Gary
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K+E=W (Knowledge Plus Experience = Wisdom.)