Posted by Hopper on 14/05/2016 02:35:12:
Apostrophe is never used to indicate plurality. Only to indicate possession or abbreviation (eg it's).
Let's not be too adamant:
The Firm's accounts …. (singular Firm)
The Firms' accounts ….. (plural Firm)
The plurality or otherwise of the Firm is indicated by the position of the apostrophe.
…. or, if you prefer to stay more on-topic:
Model Engineer's Workshop ….
Model Engineers' Workshop ….