New Ei KT90 & 6CA7 Tubes

I own a new, never used, pair of Ei KT90's. There is a sticker on the box that has 50/51 on one tube box, and 50/44 on the other tube box.
In addition, I own a new, never used, pair of Ei 6CA7's. There is a sticker on the box that has 30/28 on one box, and 30/41 on the other box.
All four boxes are yellow with red 'Ei' writing, with INDUSTRIJA written also in red. There's a blue band at the bottom of the box that has 'MAGNOVAL' written in the blue band.
These tubes have been sitting, unused in my listening room. Are these worth anyhting?
The KT-90 is a very highly sought after tube. In particular the type III look for that variation mark wherever they put it. It is not universally admired but demand is desperatley high. It is a Sturm und Drang tube that my English tube guru called timebombs. They have the ability to put out big numbers for wattage.
The 6CA7 is also valuable because it is the true fatboy type. That tube is a tetrode whereas EL34s are often described as one tube. This is untrue they do sub for each other but the EL34 is a "beam" pentode. In my amps there is an astonishing difference in the sound. With true 6CA7s which are available from EH they sing gloriously, with great dynamics, slam and authority across the bandwidth, EL34s are a mere 98lb weakling by comparison. This is only in my circuit as far as I know and not a general attribute. The only other true tetrode made these days is the reissue KT-77 which I liked but melted one of my tube sockets and are known for shorting and unreliabilty.
Thanks Mechans!
I did look more closely at the KT90's for type III designation. There is stamped on the tubes, in very small white letters, the following disignation:
Is this the type III variation mark that you are refering to?
Lastly, should I try and sell these things or swap them the next time I purchase new tubes? If so, what do think the KT90's and the 6CA7's are worth? Any idea? Anybody?