"They had a style that was different from everyone else. I've never felt that again at Eurovision," the 76-year-old pensioner told AFP.
Ingmarie Halling, who worked as the group's costume designer, explained that the eye-catching clothes were no accident.
"They decided to both be seen and heard and (decreed) 'no one should forget what we sound like and how we look,'" said Halling, who is now the curator of the ABBA museum in Stockholm.
In May, Sweden hosts the contest for the seventh time, in the southern city of Malmo.
It earned that slot after Swedish singer Loreen won last year's contest with the song "Tattoo".
The timing has presented an opportunity to celebrate the jubilee of ABBA's 1974 Eurovision victory with "Waterloo".
With their unique style and catchy melodies, the four members of ABBA -- whose initials make up the name of the group -- personified disco around the globe until they stopped performing in 1982.
Their prolific output -- eight albums in as many years -- and decision to allow journalists access to their private lives have solidified their place in the pantheon of Swedish music.
"Before Eurovision, there were both those who dismissed ABBA as commercial garbage and those who thought ABBA was great," Halling told AFP.
After the victory in Brighton on April 6, 1974, "the positive came out on top".
- 1974, a landmark year -
"They became an inspiration for many artists and musicians that you can break out internationally even if you are from little Sweden," Halling explained.
Adding to the inspiration, at the same time, small Swedish pop group Blue Swede topped US charts with their cover of "Hooked on a Feeling".
"(The year) 1974 has become somewhat of a point of reference as the start of Swedish music success internationally," Christel Valsinger, editor-in-chief of Musikindustrin.se, which specialises in the Swedish music industry, told AFP.
In ABBA's footsteps followed acts such as Roxette, Ace of Base, The Cardigans, Robyn, Avicii and Zara Larsson.
Other less recognisable names have also made an international impact.
They include composer Ludwig Goransson, who has twice won Academy Awards for best original film score, and producer Max Martin, who has collaborated with a range of pop stars from Britney Spears to The Weeknd.
Since the late 1990s, songs composed by Martin have reached the top spot in the coveted American Billboard chart 26 times -- as many as John Lennon.
He has also topped the chart 24 times as a producer.
While rarely speaking in public, Martin has said he owes his career to the Swedish system of local public music schools.
In the country's conservatories, young people can, for a modest fee, learn an instrument and the basics of music theory.
The network of popular education establishments also offers study circles, courses and workshops that provide broad access to music throughout the country, Valsinger noted.
- New technology -
In addition, "Sweden has been open to new technology", she added.
"This has created favourable conditions for Swedish music producers to quickly adopt new methods for music production."
Today, the Scandinavian country of 10.5 million inhabitants -- home to the world's number one music streaming platform Spotify -- is the third largest net exporter of music, just behind the United States and the UK.
A 2020 report by industry group Export Music Sweden noted that this was "thanks in part to the enduring and exceptional popularity of ABBA and Roxette and the number of Swedish songwriters that work with big international artists".
In 2022, revenue from the Swedish music sector topped two billion kronor ($188 million).
ABBA's popularity was rekindled by the "Mamma Mia" films, which introduced the group’s music to new generations.
The quartet has also returned to the stage through ABBA Voyage, a new album released in 2021, and a permanent show of the same name in London in which they are represented by digital avatars (holograms).
The four have sworn this will be their last collaboration.
But Halling thinks the saga may not be over.
"I'm not ruling anything out with Bjorn and Benny," she said with a smile.
Brazilian Indigenous leader, environmentalist and writer Ailton Krenak speaks with other members of the Brazilian Academy of Letters during his induction ceremony © MAURO PIMENTEL / AFP