But they had to lose in court before they paid Willie Dixon and others. I always wondered if Led Zeppelin was to blame for this, or was it their label, Atlantic Records (In the USA – I don't know what label LZ used in the UK or Europe). Record labels owned the rights to the music they recorded, and very often had a rather poor track record of fully attributing authorship of that music.
Witness the miserable story of how Atlantic Records essentially did in Stax Records of Memphis. Atlantic helped out that small label in Memphis, TN with distribution and sales until their agreement ended in 1968. Afterwards, they owned the master tapes and all the legal rights to all of Stax's recordings that Atlantic distributed. They claimed it was standard practice in the recording business, but it was ugly theft, legitimized by lawyers and obscure contract language. Stax hung on as an independent label for 5 more years, but they never recovered from Atlantic's theft.
Read more details here starting with 1968: Break with Atlantic Records.