Writer attribution for Lennon/McCartney songs 

Your edit comments that "Authorship of Beatles's songs is difficult to ascertain precisely, except for the rule that the lead singer is the dominant writer" and "Authorship of Beatles's songs is difficult to ascertain precisely, since all four, plus George Martin and others, were frequently involved in the crafting" are wrong on several counts.

 The official, legal credits are easy to determine: Lennon/McCartney except for some early songs which were originally credited to McCartney/Lennon. Ample sources exist and the WP infoboxes show the official L/M (or M/L) credit.
 Who actually wrote the song is pretty easy to determine for most of the songs where there is no dispute between L and M. Using various interviews and biographies as sources, L and M say what their part was. For a small minority of songs, such as "Eleanor Rigby", L and M disagreed and the article describes the disputed authorship. For cases where there was a 60/40 split, adverbs like "predominantly" or "mainly" make sense, but not in cases where there is no dispute that L or M was the sole author.
 While it is true that the lead singer was often the main writer of an L/M song, it is not always true. "Every Little Thing" is one such exception.
 Other people who contribute to a song—such as a producer or soloist—typically do not get a writing credit for their contribution. That's standard practice in the industry with rare exceptions, and there are good reasons for it. When someone makes a significant contribution, that should be discussed in the prose or in the Personnel section, i.e., "Martin wrote the string arrangement" or whatever.

Your position on the L/M situation is a minority viewpoint. The authorship details you are challenging are typical of hundreds of articles that have similar prose and use similar evidence and the text in those articles have been accepted by many WP editors. That represents a strong consensus for identifying the actual author in the prose. You should seek consensus for your changes and present reliable sources that support your view. —