Mysterious lump on 42023, and part number nowhere to be found!

[Phoxtane]

The thread title may be a bit unwieldy, but bear with me.

I've been cataloging my bricks via Rebrickable, and I've noticed something three times now that's caused me confusion, so I figured I'd ask. I keep coming across something very weird on part no. 42023 [slope, Curved 6x1 Inverted]. On the underside, where you'd expect to find the part number, there's a blank rectangle-shaped lump that stands out slightly from the rest of the underside. The part number is nowhere else to be found. The only similar thing I've heard of is the 'Pat Pend Removed' bricks. Can anyone shed some light on this?

Here's a picture of the part. It's fairly common. I was unable to get a proper picture of the lump in question, so I've marked the hole in the underside where it resides in red.

[Front]

I've checked a few of mine, and there is a cavity and mould number (combined), and a copyright C at the deep end of the square hole. I've checked parts from at least three moulds.

It is not absolutely necessary to have part number and LEGO name associated with the copyright C.

It does look a bit strange though, I could have fitted part number, cavity and mould number, as well as C LEGO in this area. But we do allow smaller letters than in the "old times".

Erland

Part Design