Yours is certainly the older version. If I had to guess I would say it must be at least eight years old or even older. Maybe Darker has changed the composition of the 7PC with the introduction of the plastic ball, but who knows.
Darker has only two lenses/ logos which they randomly use for their 2a hinoki blades. The blue one and the dark green/gold one. I have three new version 7p-2a Carbon blades, all have the thicker core, two have blue lenses, one (which I have bought just recently) has the green/gold one.
There's another one, a gold one, with kanji (?) characters below their logotype. That could be an even older one? Since the posts I found dated 2015 through 2021 have the blue lenses. The 2021 I found had thicker core, similar to yours.
https://forum.tennis-de-table.com/t/darker-7p2a-carbon/2180/9
Yeah, you could be right, they may have changed the composition for the plastic ball. Mine came in a very dark blue box, so if we can find out when they start using that box, we may be able to figure out when they started making thicker cores. The one on the french forum had a royal blue box... ... ... Or I'll just ask the seller tomorrow morning -.-'
What you may also want to be considering is Yinhe's level of craftsmanship and the quality of the materials they use vs Butterfly's.
However, if you want a real experience with Hinoki you should be trying something like a Darker Speed 90. Nothing feels like a 1 ply Hinoki blade. They are expensive and they break easily. But that is the real HINOKI FEEL thing. Any multiply blade with Hinoki in it is nothing in comparison to a good quality 1 ply Hinoki blade.
True... There are several other aspects that I consider as well, besides the fact that the finishing quality is higher in Butterfly's, such as endorsement fees, advertising, labor, handle designs etc. The Joyner H-II was about USD 28, had Yinhe sold one, should only cost a mere USD 18, perhaps? Had Butterfly produced a Kiso 5-ply, out of the same material that Yinhe is using, it could easily be sold at USD 60, instead of the USD 42 that Yinhe is being sold at. So I'm thinking that I did upgrade my blade from a 28 bucks blade to a 60 dollar one, and it kinda did feel that way. There was this "rumor" I found from OOAK forum, I think, from 2014, that Butterfly outsourced their manufacturing in Taiwan. He suspected it's Yinhe, if that's true, then the manufacturing quality shouldn't lagged that far behind, I guess.
It's just that Butterfly surely wouldn't be making a full Kiso blade out of a, say a 100 year-old wood, as what I suspected Yinhe did. Which is the sole reason I wanted to own a higher quality Kiso blade...well, other than how gorgeous those Darker blades are lol. Though I am a tad disappointed with mine, the logo on the handle and on the bottom of it, the J.T.T.A stamp, and the misaligned top of the handles FH and BH side. But overall, a much better finish than the Jonyer H-II.
I've read plenty of your comments about how fragile those one-plies can be though, hence I stayed away. The Speed 90 is way too expensive for me, I was also tempted to get Nittaku Miyabi instead, but considering how soft these Kisos are...nope.
I've really enjoyed the Yinhe Kiso 5, though. I'll settle for a multi-plies Kiso, I guess. Trying to figure out how this 7p-2a carbon actually behaves, whilst also hoping to find more infos on the actual properties of the Kiso itself.