need help with shanling t100 please

hi, i've heard rave reviews about changing the tubes in the shanling to we, i just got two we 396a tubes. here's the thing, both have yellow writing, but one says just 396a on it, and the other says 251/396a. they weren't tested..and assuming the diff numbers mean different dates or you guys who have tried these tubes think it will matter if they arent matched? i put them in and they sounded screechingly bright and lacked bass which is the opposite of what i've heard they should do. do you think this is that a mismatch issue, or a break in issue? any help would be appreciated. thanks;)
I had the same unit (Shanling) sent to me as a review sample and I replaced the stock tubes with Western Electric 396, supposedly the best version of this tube ever made.

The WE's I received were a matched pair, new in the original box and my results were certainly different than yours. I heard no difference between the super NOS WE's and the stock tubes.

To directly answer your question, I don't think there is a problem with the tubes being marked differently, the 2C51 is a sub number for the 396 according to my tube substitution handbook and not at all that uncommon to find them marked both ways.

Good luck with the tweaking.