Use them for ends at the wall for starters or end pieces. Of for kindling for the fireplace (lol). You more than likely will end up with about 25 - 30% waste as it is.

25% waste sounds high to me, do you really expect that much? My flooring guy usually orders about 5 - 6% extra. That seemed low, so I ordered a bit over 10% extra. Another 4% is "less-picky" areas -- under range, refrigerator, in pantry.

25% is extremely high. Unless its prefinish from home depot. 10% is good for a novice installer.

The damaged pieces can be used in the field. I suggest you dont use them together spread them out. Ideally if you are installin in a kitchen use the bad pieces under cabinets or closets/pantrys.

You could also save those pieces for any future replacements seein as how you would just cut the grooves off anyways for splicing.

Another question along the same line -- are the tongue and grooves on unfinished hardwood "standardized," such that flooring from different manufacturers might be expected to fit together?

Some have a standard. But each mill has its own way of milling each piece. While the demensions may be the same (3/4") the groove may be off just enough to where the tongue of a different mill may not fit. But sometimes you can get lucky.

So it is really a toss up. But i would really just play it safe and say no.