This 2LP set is in fact a compilation of the 2nd and 3rd albums:
(1971) and
(1973)
It seems that this 2LP set was original issue, may be at the same time with 2nd album (sides A and B of this one).
Two years later sides C and D published as 3rd LP with additional track A9.
Compilation usually can not include album published 2 years later.