Datasheets and probability

Hi, men -
There are sometimes 3 columns on a datasheet which may contain min, nom, and max values. Like Vds for example.
Is there any probability tacitly assigned to the values? I know that nominal is the average, and I assume that the value lies between the two middle one standard deviation points.
1. Is that a valid assumption?
2. Is the min between one and two standard deviations down from the mean?
Thanks and I apologize for asking such a basic question in this professional group.
Cheers,
John