Didn't Abba's So Long flop? - Hence why it was never shown on TOTP.
Also by the middle of 1976 I think Abba had become so big that they wouldn't have had time to do many music shows - hence why they made the videos - so they could circulate them round the world!
'So Long' did indeed not make the Top 50 - but it definitely featured on TOTP as a new release. There are clips on Youtube - it really did happen, Tortfeasor, I remember it!