All products produced by a given company will use the same GS1 Manufacturer Code.
EAN-13 uses what is called "variable-length manufacturer codes." Assigning fixed-length 5-digit manufacturer codes, as the UCC has done until recently, means that each manufacturer can have up to 99,999 product codes--and many manufacturers don't have that many products, which means hundreds or even thousands of potential product codes are being wasted on manufacturers that only have a few products. Thus if a potential manufacturer knows that it is only going to produce a few products, EAN-13 may issue it a longer manufacturer code, leaving less space for the product code. This results in more efficient use of the available manufacturer and product codes.
In ISBN and ISSN, this component is used to identify the language in which the publication was issued and managed by a transnational agency covering several countries, or to identify the country where the legal deposits are made by a publisher registered with a national agency, and it is further subdivided any allocating subblocks for publishers; many countries have several prefixes allocated in the ISSN and ISBN registries.