I added about 1/4 quart of the same type of oil but forgot to check the milage. Will this matter as long as I mention the top off on the form when I get the oil analyzed?
Not really, unless you're draining it tomorrow. Rough estimate is fine. IMHO if you only added 1/4 quart you probably didn't even need to, unless you're really, really picky. No need to add til you're at the bottom end of the "safe" area.