This map seems to use a very variable and at times generous definition of both “company” and “still in business”.
Sure, Australia Post is one of Australia’s oldest institutions if you count from the date of the establishment of its oldest predecessor (which this map does, as a Postmaster-General was first appointed for New South Wales in 1809), but a single national postal service wasn’t established until Australia itself was established in 1901 and the colonial postal services were merged, and even then it was a government department until 1975, and wasn’t corporatised until 1989 and remains government-owned to this day.
Reminds me how the restaurant Earl of Sandwich, which was founded in 2004 in Orlando, puts established in 1762 on their website and the front of some of their buildings [1]. Just because the "sandwich" was invented in 1762.
It's similar to how Carlton claim to have been around since 1832 (when in fact they were founded in 1903[1]). The fact is that their subsidiary Cascade has been around since 1832 but were bought out by Carlton much later[2], therefore making the claim that Carlton is the "oldest brewery in Australia".
[2]I can't find a reference to which year they were bought out, but the Wikipedia article above does mention they got bought and they mentioned the year when I took a tour of the Hobart brewery.
Likewise the "oldest" company in El Salvador is HSBC... the Hong Kong and Shanghai Bank. I mean that might be the oldest surviving locally registered corporation on the books, but it kinda wastes a chance to learn something interesting about the country.
Sure, Australia Post is one of Australia’s oldest institutions if you count from the date of the establishment of its oldest predecessor (which this map does, as a Postmaster-General was first appointed for New South Wales in 1809), but a single national postal service wasn’t established until Australia itself was established in 1901 and the colonial postal services were merged, and even then it was a government department until 1975, and wasn’t corporatised until 1989 and remains government-owned to this day.