There is a continual effort to fix mismatches in the data. For example locating places where the same song or artist is listed under multiple different names. One user pointed out that "Riders in the Sky" and "Ghost Riders in the Sky" were actually the same song (for which thanks). The source charts were edited to ensure that the same name was used everywhere, when the next version was generated the song went from being at numbers 6 & 7 of 1949 to being the number 1 song of the year.
So the movement of songs and albums in the charts is often a valid result of improvements in the source data.
You may also notice some artists come and go as these type of corrections adjust their total scores. This site lists the all the hits of the top 1000 artists, so if an artist moves from, say position 998 to 1002 in the list their songs will no longer be listed here. When new charts are added, or when the names of artists are consolidated a few artists and songs will come into the lists and matching number will drop out of them.
Previous Comments (newest first)
15 Jun 2018
I have noticed that'Rock Around The Clock' has moved twice on all-time charts,the position was like 2-??-5 or something？ This site has not many charts(compare to 00s) in 1950s,I wonder what you guys have calculated the score of this song,so it reached #2 before,and then what made this song dropped,and rose again?? ALSO,the ranking of Poker Face on 00s chart: 2-1-2,(meanwhile Yeah!1-2-1) So as 90s chart:Everything I Do:1-3-1
This FAQ explains why songs move. Usually this is because the data is extended or corrected. Occasionally this is because the scoring parameters have been adjusted. That requires that we all agree that the new parameters fix some existing prolem and don't cause any obvious issues elsewhere.
Remember every parameter is a compromise, we just have to adjust them to get the result as good as we can.
29 Mar 2013
Did a bootleg ever chart, is there a possibility of that?
It depends on which chart you are talking about. The Billboard and UK charts are based on "official" sources (record sales and radio plays) so it is unlikely that a true bootleg would show up.
There have been many "official bootlegs" that have charted somewhere, mostly from the late 1990s or early 2000s.
More bootleg albums have made it into the album charts, Bob Dylan, for example has had 8 bootleg albums in the charts.