SES still has Werther listed on her stallion roster. It’s not expensive, and likely has been in storage at Celle for some time. I’m not sure that means much of anything in relation to semen quality… but is something to be aware of.
I didn’t read the other post carefully… but … be aware of WFFS. Have your mare tested. I don’t know what Werther’s status is, and to my knowledge, it hasn’t been published, but Wolkenstein II is a carrier, and Wendekreis was his dam sire. He has G line in his pedigree too though, and some of the G line stallions are carriers. So maybe that’s the source. Whatever the case… make sure you look into this issue and get your mare tested before pursuing breeding with older unknown frozen semen like this.
Also, given the affordability of the Werhter doses, and their age, if I were in your shoes, I’d consider buying a dose or two of another option as well. If it’s all coming from Celle via SES, there are other good options with more info concerning semen quality and recent usage 
FWIW though - I like a lot of the old stallions and the prices are affordable, and I debate the idea of creating a keeper from something old fashioned regularly. I enjoy looking at the stallion info, and it’s fun to think about. My fixation is more on the G line stallions though.