Only users with access to Google My Business Locations can view all locations, consumers are limited results that are local to them. You can however view other areas by doing a business name + name of area search.

Should be also noted that it is common for Google to return other businesses despite users not including them in their search, this is due to the fact Google likes to provide users with options. For example, if you search "Tesco Bournemouth", you can expect "Sainsbury's" to be shown on the map too, this is due to the fact they are relevant to what the user is looking for.

But other businesses don't need to be so relevant either, because Google may decide that you are looking for things to do and visit, so it includes other companies such as Coffee shops and other local businesses. Google Maps is NOT there to serve your 'Clients' business goals, it's purpose is to return results that are helpful, this includes all the other things I just mentioned.