Master Technika... over the hill...

[AeroTechnika]

I have a classic Linhof-type 75mm Biogon which is 415x,xxx, and a USAF-type 75mm Biogon which is 451x,xxx, and looks exactly like the one in the Master Technika picture in the OP, so they must have been made later as well.
It is worth noting that the glass geometry is very different between these two types, with the meniscus curve on the front and rear elements of the Zeiss/Linhof much deeper and more pronounced than that on the USAF version.

[Embdude]

I have a classic Linhof-type 75mm Biogon which is 415x,xxx, and a USAF-type 75mm Biogon which is 451x,xxx, and looks exactly like the one in the Master Technika picture in the OP, so they must have been made later as well.
It is worth noting that the glass geometry is very different between these two types, with the meniscus curve on the front and rear elements of the Zeiss/Linhof much deeper and more pronounced than that on the USAF version.

That is a good observation, first time I have heard of a difference with the glass between these lenses.

[AeroTechnika]

I'll see if I can get a side-by-side picture to show the difference.

[Embdude]

I'll see if I can get a side-by-side picture to show the difference.

That would be great, I would love to see that!

[David Lindquist]

That would be great, I would love to see that!

I would too!

David