Custom imprinting pens for stationers, department stores and businesses goes back almost to the very beginning of the industrialized steel dip pen. Some of these customers were as small as a stationer who wanted their own name on the pens, but some customers actually had pens made with their name on it, and created whole companies and brands around it. Spencerian Pens in the US is one of the best known. That was a brand of the New York Stationer Ivison Phinney and Company (there were several variations on Ivison's name as partners came and went over the years). They sold millions of Spencerian Pens over their 100+ years, but they never actually made a single one. The pens, for most of the company's history, were made in England by first Josiah Mason, and later, when he split from Perry, by Perry. (technically, in the 1870s, a few of the Spencerian pens were made by Gillott, with most made by Mason, but that was short-lived)
What you may have are some pens all made by the same pen factory, but just stamped with a different, custom imprint. I looked up Belman in People, Pens and Production, the definitive book on the Birmingham pen industry, and they're only listed with no other information.
P. Belman & Co. (& Son Ltd 1923)
73 Pershore Street 1903-1910
73 & 75 Pershore Street 1911-1919
22 Bromsgrove Steet 1920-1940
So, your pens marked Belman & Son can be dated between 1923-1940. Most surviving dip pens today survived because they were shoved into the backs of drawers when their owners got their first fountain pen and kept around the old pens "just in case." So, most surviving vintage pens are from about 1920s onward. I suspect the "Hart" was a stationers or department store or even a hotel or other business where the public might be supplied a pen to write a note or sign a document. They may have purchased the pens from Belman, liked them, and had Belman make some with their custom imprint.
Interesting! Any pictures?
