Friso Kramer Result chair variations  

Hi All,
I recently received a couple of Friso Kramer Result chairs and I noticed a couple variations.
1: version a, oldest one I think, round 'Ahrend De Cirkel' logo on metal of backrest. thicker wood, slightly different backrest shape than newer versions
2: version b, current Ahrend logo on metal under seat, thinner wood, slightly different shape of backrest
3: version c, no logos whatsoever. wood has same shape as version b. the varnish of the seat has some sort of textured effect, it's not just smooth and glossy.
The backrests of version b and c both have 60-05 embossed in the varnish on the backside of the back rest.
can someone enlighten me on these versions? when did the second version come in to production? is the 3rd version, without the branding a special production? Did Ahrend even produce Result chairs without embossed branding? The textured varnish, was that some sort of finishing option?
I'd like to find out as much as possible, so any info is welcome.
Thanks in advance