RARE German Bundeswehr M35-50 1951 BSG Helmet of named Spanish Guard Volunteer

This is a rare and unique German Bundeswehr M35-50 helmet. Featuring only vent holes, this variant of the M35 was issued briefly as WWII was winding down and given to western border guards of the BSG for a short period around 1950-1951 before the military transitioned to the solid shell helmet M35-53 and newer models. The helmet is a size 62 as indicated inside the back side. The liner inside is marked as a size 53-57. This helmet has a distinctive liner that is not attached to a ring at the rim but instead is connected to the inside of the helmet dome with prongs meeting at the inside peak under a padded main attachment, and lined with a tanned, 8-flap leather lining secured with a boot-string-like cord. I was unable to remove the liner to check for the manufacturer of this particular helmet, but there is no other marker on any exposed areas inside the shell, so I do not know which supplier made it for the officers of the border guard.
While I was trying to figure this out, I noticed

Product Information