I have a terrible, terrible confession to make

Your honesty, iiwftn, does you credit. But it's not a terrible confession.  I remember once reading comments on YouTube about Andante Andante and someone stating something to the effect that what a beautiful, sensuous vocal it was by Agnetha, and someone else pointing out that it was Frida on lead.

Although, I don't think I've got it wrong about their leads, I do think their combined singing isn't always as it seems - or at least occasionally I get a probably false impression of what was really happening between them vocally. For example, Fernando strikes me as mostly Frida: the lead and the upper and lower harmonies. Probably totally mistaken, but I think I detect her vocal nuances in those harmonies on the recording.

But then again, Agnetha and Frida were likely so adept at matching up their singing to each other that I think it's not always easy to discern who sang what on a track when it comes to their non-lead combined vocals.

For quite a while from its release, I thought it was Agnetha singing the closing lines of The Visitors (“I have been waiting for these visitors”). In fact, I seem to want to think it’s her now, even though I know it isn’t.

Similarly I’d always thought it was Agnetha doing the “La La La” vocals on Move On. But then someone on a previous forum said it was Frida. I’m now not sure what to think - is it both of them? Agnetha was pregnant when they were making The Album, and had to lie on the floor to record some vocals. Frida had to compensate in places.

The above examples are possibly because both Frida and Agnetha were capable of mimicking the other to some extent. Agnetha could sing lower than her normal register and Frida could sing higher than hers.

I still hear You Owe Me One as a Frida lead, whatever anyone else says (though it’s hardly a glorious addition to ‘her’ tracks). That also goes some way to balancing out the lead vocals on the 1982 songs.

I always heard Our Last Summer as Frida, but my terrible confession was that I used to think of On And On And On as an Agnetha lead. That made sense, as it balanced out the lead vocals on Super Trouper. But of course Frida actually has one more lead than Agnetha on that album.

As a child I played Greatest Hits Vol. 2 to death, and was convinced for years that 'I Wonder (Departure)' was an Agnetha lead. 40+ years later and I wonder how I could ever NOT hear it was Frida's voice. All I can think is that it was maybe the 'soft innocence' of her singing that particular song.

What about Kisses of Fire? I think the original album stated it as an Agnetha lead, but in reality she only sings the first verse solo. The second verse and chorus are both of them aren’t they? Or is Agnetha just singing the second verse in a different way from normal?

Not sure there are many songs in ABBA’s catalogue where the first and second verses are so different, other than the melody. The first verse is a ballad, whilst the second is given the full-on disco treatment.

The verses of TACOM ("we can go dancing/we can go walking" etc) always sounded to me like they were sung by Frida, but the filmed performances show them as joint vocals. Likewise, the "Sorry, Cassandra, I misunderstood" line sounds like it's sung by Agnetha, but it's both of them.

Even though lead vocalists have been officially credited, some songs really only have short solo passages before The Third Voice or close harmonising kicks in. I think it underscores that ABBA is a group of equals, and not a lead singer with three back-ups band members. It makes ABBA greater than the sum of its parts.

I agree, Tony. I don't think their filmed performances always accurately reflect the studio recordings, either. This is the case with Fernando, imo, but of course I'm not referring to live performances of the song.
And, yes, what gets characterised as a lead can be just a short solo vocal on a track that really is largely a joint vocal, or multi-layered vocals.

My pitiful misapprehension would have to be that, until embarrassingly recently, I never realised who was doing the lead vocal on 'Suzy-Hang-Around'. In my defence, I hardly ever listen to the 'Waterloo' album and my ears have glazed over (??) long before we get to the final track.