The discussed daisho is for sure an above average example.
The Soten school at a certain point in time was so popular that other workshops in Kyoto and Nagoya (citing from memory) started to produce pieces in the style, or so it seems from the common lore.
Some signed as soten others mumei with a large variation of quality, from very crude to high quality. Tsuba from the school proper (first, second and maybe third generation) are extremely rare. Most of example we see are at best "in the style of" from other workshops.
I have by now amassed a database of a hundred referenced pieces. NBTHK papers are basically useless they seems to only certify thet a tsuba is not a modern fake, no information is given about anything.
Also from mei comparison no conclusion either, the variation is staggering.
It is a mess...
Regards
Luca