Most "Best Of", or "Greatest Hits", albums, by any artist, differ from one another in their list of songs. You really should check sites that have lots of reviews when buying albums, or anything for that matter, even if you aren't planning on buying them from the site. Amazon is one of the best product review sites around. Just go there and do a search for Glen Campbell. Then check out the various "Best Of" or "Greatest Hits" albums for the reviews. Anthology albums or box sets of course have the most complete selections of songs for a particular artist.
...of course, simply checking out the various albums or CDs on Amazon or wherever you will learn what songs are included on them. The reason for checking the reviews is to gather additional details about the album, such as quality of the tracks (remastered or not), length of the tracks (are the tracks cut short?), are they the particular version of the song you are looking for (remake or not by same artist), etc. You may also get suggestions for a better choice of a “Best Hits” album for that artist. Plus lots of other helpful info similar to this.