Mazari palm (Nannorrhops) - silver form from Pakistan

[PAPalmGrower]

I recently read the article "Nannorrhops, the Enigmatic Palm" by Robert Lackner, published in Chamaerops No. 45 online. The different forms of Nannorrhops are mentioned - although many lump them all together under 'Nannorrhops ritchieana' - the different forms look and behave somewhat differently.  Robert mentions that the blue Pakistan form (also offered as N. ritchieana 'silver form') is different than the silver form from Iran (referred to as Nannorrhops 'arabica'). He says that the Pakistan blue/silver form (N. ritchieana 'silver form') is by far the least cold hardy, even less so than the 'arabica' from Iran.

I can't find any other sources online that support this - the other sources all say that the 'arabica' from Iran is the least cold hardy.  Obviously, provinance of the original seed source, winter moisture, duration of cold, frequency of snowfall, etc. play into this, but does anyone else have experience growing the blue/silver form of ritchieana from Pakistan?  Is is markedly less cold hardy than the 'arabica' from Iran?  or, is it the other way around?  Any info that you could share would be greatly appreciated.

(As a side note, I lost an Iran 'arabica' last year under fairly dry conditions at 26 F/-3 C, which led me to believe it was not the hardy one.)