The Mellotron Group

From the Mellotron tape library http://www.mikedickson.org.uk/tron/
under Other Sounds and Services:

" Standard three track tapes have always offered two additional blends at the mid points between A and B and B and C but now you can have 5 unique voices from the new 6 track format. "

Here's what I think:

position A - voice one

position AB - voice two

position B - voice three

position BC - voice four

position C - voice five

You would also be able to dial in four different "mixed voices" between these five selector positions.  How bloody marvelous is that?!!