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Tough call. I see your difficulty. The spermatheca doesn't look like kahlenbergi, more like verdezi or vagans.
But then judging by coloration it looks least typical of vagans, more like verdezi or kahlenbergi.
I know: spermatheca trumps coloration. But then vagans is by far the most common in the hobby, but... I am confused and don't know.
Drat! Come on, DaveM! Never! We must never, never on AB must anyone admit not knowing something. OK, got it: it's a hybrid. For sure: it's a hybrid. Wild-caught? Yes. So, yes, obviously, a hybrid. I knew it all along.
Sorry I couldn't help you better.

OK, when and where did you purchase this spider?

I'm not good at dealing with failure, so here are my best answers:
1) If it's wild-caught, that is verdezi. Range is close to kahlenbergi's; there was just a little mixup.
2) If it is captive-bred by a reputable European breeder, then it is kahlenbergi. She's not full grown, and even though your picture appears excellent, you might be deforming the spermatheca a little bit. When she grows a little more, and when the spermatheca isn't held up at an angle, the lateral lobes will appear more pointed.
3) If you bought it from a totally unscrupulous person in an alley, who was puffing a foul-smelling cigar into the face of the baby he was carrying, while spitting and making offensive comments to passersby: then it is vagans, and you've been cheated!

In any case, the colors look washed out, a bit atypical, and maybe a molt will fix that.

The photo is six months old. It's two days after molt. When he leaves the nest, I take a picture

"Die bei SCHIMIDT (2003) abgebildetete Spermathek von B.verdezi, beruht auf einem falschen Tier. Er hat hier das Genital von B. schroederi abgebildet. Die Spermathek von B. verdezi entspricht der, welche ich in meiner Arbeit über B. schroederi als Brachypelma sp. (RUDLOFF, 2003) abgebildet habe (Abb. 25). Sie ist sehr hoch aufgewölbt und erinnen ventral betrachtet sehr stark an B. sabulosum,..."

Rudloff, J.-P. (2008b). Eine neue Brachypelma-Art aus Mexiko (Araneae: Mygalomorphae: Theraphosidae: Theraphosinae). Arthropoda 16(2): 26-30.

This means B verdezi should have a higher domed spermathecae without this median depression.
Therefore the shown picture has more similarities with B. kahlenbergi.

c.h.esteban said:

"Die bei SCHIMIDT (2003) abgebildetete Spermathek von B.verdezi, beruht auf einem falschen Tier. Er hat hier das Genital von B. schroederi abgebildet. Die Spermathek von B. verdezi entspricht der, welche ich in meiner Arbeit über B. schroederi als Brachypelma sp. (RUDLOFF, 2003) abgebildet habe (Abb. 25). Sie ist sehr hoch aufgewölbt und erinnen ventral betrachtet sehr stark an B. sabulosum,..."

Rudloff, J.-P. (2008b). Eine neue Brachypelma-Art aus Mexiko (Araneae: Mygalomorphae: Theraphosidae: Theraphosinae). Arthropoda 16(2): 26-30.

This means B verdezi should have a higher domed spermathecae without this median depression.
Therefore the shown picture has more similarities with B. kahlenbergi.

Click to expand...

Check the photograph in plate #9 of the Rudloff paper you cite, and you will see that kahlenbergi has a much deeper central dip, less rounded lateral lobes (more like hilltops), and no whitish peak in the center.
Mendoza & Francke 2020 is also somewhat helpful for rejecting other species.
I'm not discounting kahlenbergi as a possibility. Maybe when the spider grows further, it will be more clear.

See Schmidt 2003. The spermatheca posted above really looks a lot like verdezi.

@DaveM

Do you have translate what i quote from RUDLOFF?

The summary is that SCHMIDT make a mistake (unfortunately not the only one)!

The spermathecae that he shown as verdezi in the Fig. 2 (Schmidt, G. (2003g). Das Männchen von Brachypelma verdezi sp. n. (Araneae: Theraphosidae: Theraphosinae), einer häufig mit Aphonopelma pallidum verwechselten Vogelspinnenart aus Mexico. Tarantulas of the World 86: 4-9. (also 87: 4-9)) was from B. schroederi.