It says they recorded a Swedish version of Chiquitita, but I've never heard anything about that. It also seems to be saying ABBA as a group recorded a Swedish version of Fernando, but I'm not aware of that, although I'm well aware of Frida's solo Swedish version.
I love a list. But the weasel word is (of course - as ever) 'best'. For me, my list of ABBA's 'best' songs would differ significantly from a list of 'my favourite' ABBA songs - and indeed from my list of 'ABBA songs I listen to most frequently'. Three different lists.
For instance, I'd happily place TWTIA in the first of those three lists, but certainly wouldn't include it in the second or third. It's clearly a great song, but not one that I'm especially mad about or that I listen to very often. It's ABBA's 'Stairway to Heaven', perhaps. Undeniably epic, accomplished and 'influential', but give me a straight choice right now and I'd much rather listen to 'In the Evening'.
To be fair to the Billboard list, I'd support the inclusion of around half of those songs cited as valid claimants to a place in a 'best' of ABBA selection.
Waterloo: "An early song in ABBA's career, the 1974 single incorporated rock and jazz elements"
I don't hear any jazz elements like unusual time signatures or some sort like that. The only thing jazzy about Waterloo is the brass/woodwinds sections. Otherwise, it sounds more like 1950s "rock and roll" with synthesizers and borderline bluesy to me. One time I read somewhere that ABBA was allegedly inspired by Wizzard's "See My Baby Jive", which isn't "jazz", but more like a Spector-like rock kind...