It seems like this mold had (at least) two life phases. Initially the logos were in the normal position, later they turned sideways.
The transparent and black bricks on the top left are CA, the third brick is ABS. The white, yellow, red and blue bricks with sideways logo also are ABS. The transparent brick in the top right is CA again, but I think that is because raw ABS is milky white, so an alternative plastic was needed for transparent bricks. Also, the exact moment of transition from CA to ABS was not exactly the same for all colors because all supplies of the old material were used.
Looking at small details, I am certain that these originate in the same mold (or, at least, the same mold for the inside of the bricks).
Logo: Narrow Round O logo. Initially in normal orientation, later sideways.
Material: ABS and CA.
Inner ribs: none.
Inner tubes: with rounded bottom.
Flowrib / center line inside top surface: No.
Mold pip: Just above the center on the short side, leaving a smaller mark than on most bricks.
Mold number: None.
Mold position numbers: 1 to 20, below the left tube.
Intellectual property protection: Pat. pend, above and below center tube.
Design ID (3001): No.
- sideways logo on later bricks
- CA, normal logo Black, Transparent
- ABS, normal logo White, Red, Yellow, Blue, Black
- ABS, sideways logo White, Red, Blue, Black
- CA, sideways logo Transparent
Detail Position 1
Comparing two bricks. The white brick is ABS with sideways logos, the black brick is CA with regular logo’s. There are several small details that match and prove that these bricks were made in the same mold.
The baseplate on the background is upside down, but for now I’ll leave it like that because I had not noticed the logo in the top row before 🙂
[Original post and comments on Flickr.]