[Brightcolours]

I'm still unconvinced myself, though careful tests could prove this.

Removal of VC is a mechanical change AFAIK - the corresponding element(s) stay in place, but in a fixed position.

 

As for the optics, there are differences in the published specs for the "original"  Tamron and the Pentax version. For example, the Pentax skips the front two "high refracting" elements, and an aspherical element is instead noted as "anomalous dispersion glass aspherical lens". See the links below:

http://www.ricoh-imaging.co.jp/japan/pro..._03_en.jpg

http://www.lenstip.com/340.3-Lens_review...ation.html

 

But is it enough to be called "proof"?

Pentax just chose to not label the two elements as "high refractive". The optics are the same. You can't just use different refractive glass but keep the design the same.