Oil Changes and "X000 Mile Service Performed" on CarFax

1) When I read a carfax and it shows, 5,000 or 10,000 or 90,000 miles service performed... do those automatically include oil changes? Or would carfax explicitly say if an oil change was done at those times?

2) When there are gaps in oil changes shown on carfax (yes I know someone can change their own oil and it won't show there), when are the critical times in an engine's life that gaps could more likely cause future problems? Or are any gaps horrid...?