It's a sound system thing. They used to play the vocal version of a tune (called pt1)...jack it up a couple of times (if it was popular) and then play the instrumental version on the flip (called pt2). This would allow the sound system DJs & singers to line up and do their thing over the riddim track.
Massive rewind at 21s vv although ironically they used to lift the needle straight up (like Blackmarket)
i reload is very much acceptable when say a dj double drops one his new dubs for the crowds reaction and it then it goess offf.... sooo chchchchchch -rewiiiinddddd and then starts the tune by itself from the beginning.... i think it adds so much anticipation and energy but thats me