Here are a couple Mark I knives. These were obviously issued before the Mark IIs. The Mark Is were found to be not robust enough for some uses, which prompted the re-design to the Mark II.

The Right Hand knife is a Robeson ShurEdge No20. 5-1/8" Blade, stacked leather disc handle.
The Left Hand knife is a PAL RH35 USN Mark I. 4-3/4: blade, stacked leather handle with plastic spacers. Below the photo of the full knives I flipped the knives and took a photo of the marking on the other side of the ricasso.