The story of red and green BASF is as follows: The red LH super was
introduced in late 1973. It was BASF's first superferric, and it was
also compatible with recorders that were aligned to the DIN reference
tape. (1 or 2 years later, a batch of LH super was chosen as new DIN
reference tape). This was before the international standardization by
the IEC, and the Japanese industry couldn't care less. They developed
tapes like TDK Audua and Maxell UD-XL, which required higher bias than
the DIN standard, and the cassette deck world was split into two leagues:
European manufacturers would align their decks to the DIN standard,
while Japanese manufacturers chose their favourite TDK or Maxell tape to
have their decks aligned to. As a result, European tapes sounded dull on
Japanese decks, and Japanese tapes sounded a tad too bright on European
decks. If you recorded with Dolby, things got even worse, because the
sensitivity was also different.
In 1977/78, the European tape makers decided to offer tow different
kinds of superferrics: One for European decks, one for Japanese decks.
Agfa, BASF and Philips had tapes with and without "I" or "1" in their
line-ups at the same time for a few years. The 1/I versions were those
for Japanese decks, with higher sensitivity and higher bias requirement.
BASF achieved this by cobalt doping the ferric oxide. I don't know what
Agfa and Philips did to enhance their formulas.
When a batch of ferro super LH I was chosen as IEC I reference tape in
1979, even European tapedeck makers would align to that standard, and
the older DIN-compatible tapes soon became obsolete. BASF stopped making
the red ferro super LH in 1981 or 82. Its unofficial replacement, the LH
extra I, was compatible to the new standard.