As of 1980, the adventures published were:
B1 In Search of the Unknown
B2 Keep on the Borderlands
Both for Basic D&D, levels 1-3, and were often used at the same time. (B2 had a Cave of the Unknown into which B1 was often inserted.)
G1 Steading of the Hill Giant Chief
G2 The Glacial Rift of the Front Giant Jarl
G3 Hall of the Fire Giant King
D1 Descent into the Depths of the Earth
D2 The Shrine of the Kuo-Toa
D3 Vault of the Drow
Q1 Queen of the Demonweb Pits
Were a definite series for characters from 8th to 14th level.
S1 Tomb of Horrors - for levels 10 to 14
S2 White Plume Mountain - for level 5 to 10
S3 Expedition to Barrier Peak - for levels 8 to 12
C1 The Hidden Shrine of Tomoachan - for levels 5 to 7
C2 Ghost Tower of Inverness - for levels 5 to 7
Were all unrelated
T1 Village of Hommlet was designed for Introductary AD&D characters, but was a heck of a lot tougher than the 'B' modules.
So a decent order of play would have been...
1. B1/B2 in conjunction
2. T1
3. C1/C2 in whichever order makes the most sense to the DM
4. S2
5. S3
6. GDQ series
7. S1
R.A.