About Seiunsha from Wikipedia:
"The company is entrusted with the distribution operations of small and medium-sized publishers who do not have accounts with publishing agencies due to circumstances..."
"Seiunsha does not engage in sales promotion or in-house editing."
"...the publisher's name is written on the back of books published through account lending, and the name of Seiunsha is written on the publisher's name."

Seisunsha acts as a sales agency and many companies work with them.

You may see digital stores list the publisher for print releases alternately under the name Suiseisha or Seisunsha. They are all correct even if only one of them. You may put them separately or use Seiunsha/Suiseisha together to avoid the confusion. But it is recommended to use the latter because it indicates they are working together on production and does not need to take up space with Seiunsha (print) Suiseisha (print) style which makes them like an entirely different publisher. Also, do not use labels for print. Serialization distribution is done via digital/magazine, just use this instead.