The practice of 'covering up' a record can be traced back to the early Jamaican DJs, who actually scratched out the artist/title on the labels of certain R'n'B 78's they had purchased in America, in order to keep the sound 'secret'. In theory, by doing this they could then have the track as an exclusive for longer and make their sound-system THE one to go and see/listen to.
The Northern Soul scene picked up on this too, albeit a piece of paper was usually taped in position over the label, rather than defacing it! Again, this helps the DJ keep a sound exclusive, and hopefully elusive...and this is possibly even more relevant today, considering the access to information over the internet!
Some folk don't like it, and say it stops the artist getting the attention they deserve...maybe, but...in the majority of cases the interest in the track increases (if the tune is good enough in the first place), so when it is finally uncovered the artists become sort after. Of course, the disc has to be good enough and obscure enough in the first place to warrant being covered up, and anyone covering up a disc well known to collectors also risks the embarrassent of a lack of knowledge! The longest running cover up was, 'The Del Larks' (Mello Souls - Mello) which stayed a mystery from 1986 through to the late 1990's...a minimum of 12 years!
Now take these links below to view 650+ titles (updated June 2013) that may be well known now, but once upon a time were the latest discovery! They are listed in the following order, and please note the years stated are open to correction...feel free to email me:
400+ tracks & their original scene names & titles