The beatles used throwaway lyrics most of the time. They got the chord progression, the melody, and the hook of the song together and mainly just hummed the melody until they would come up with a line the really liked. After that the used throwaway lyrics (words that fit the cadence of how they wanted the lyric to flow...but don't mean anything at all) to get lyrics going. Then as they got more lyrical ideas they replaced the throwaway lyrics with lyrics that had meaning.
The line in "hey Jude": "The movement you need is on your shoulder" was a throw away lyric that Paul had trouble replacing. John told him "you're not replacing that, it's the best line in the whole f***ing song"
That 3 part beatles special has some great songwriting footage.
Paul creating "Get Back" from scratch. George offering "something in the way she moves". He was humming much of it. On the bridge he didn't have "you're asking me will our love grow" but he already had "I don't know...I don't know" so he was using the throw a way line "sister Flow has missed the show...I don't know I don't know."
And he had "attracts me like a pomegranate" in place of "attracts me like no other lover" lol.
That footage is amazing to watch!
I think that's one thing that made the beatles songs flow so good is them getting the melody, chord progression, and arrangement together while filling in with throwaway lyrics before sweating over just the right lyric.
In my case, getting stumped on a lyric sometimes has killed the creation of the whole song.
Throw a way lyrics help to keep the process going and completely develope the tune...THEN....fine tuning the lyric can be focused on in the final stages.