This is what I dug up from
www.riaa.com, searching for all releases under both No Limit Records and Priority Records and filtering out album releases:
C-Murder: Life or Death - Platinum
Fiend: There's One in Every Family - Gold
Kane & Abel: Am I My Brother's Keeper? - Gold
Master P: Ice Cream Man - Platinum
Master P: Ghetto D - 2X Platinum
I Got the Hook-Up! (soundtrack) - Platinum
Mia X: Unlady Like - Gold
Mystikal: Unpredictable - Platinum
Mystikal: Ghetto Fabulous - Platinum
Snoop Dogg: Da Game Is to Be Sold, Not to Be Told - 2X Platinum
TRU: Tru 2 Da Game - Platinum
Down South Hustlers (compilation) - Gold
Mean Green Major Players (compilation) - Gold
Young Bleed: My Balls and My Word - Gold
Lil' Romeo: Lil' Romeo - Gold
Master P: MP Da Last Don - 4X Platinum
Master P: Only God Can Judge Me - Gold
Master P: Ghetto Postage - Gold
C-Murder: Bossalinie - Gold
Silkk the Shocker: Charge It 2 Da Game - Platinum
Silkk the Shocker: Made Man - Platinum
TRU: Da Crime Family - Gold
504 Boyz: Goodfellas - Gold
West Coast Bad Boyz II (compilation) - Gold
I'm Bout It (soundtrack) - Gold
Snoop Dogg: No Limit Top Dogg - Platinum
All of these adds up to 24 million albums up to date, nationwide. It's definitely something to be proud of, but it's still far from the 70 million albums suggested in another post, plus I wouldn't say it constitutes "ruling" over a timespan, although they did sell roughly half of their 24 million albums in 1998, competing for one of the more successful rap labels for that year.