Can't remember too many early JP's (of any big size) from 1st couple of credits.
However I do remember the most surprising JP I've ever won. Playing Club Snakes and Ladders (I think, the Barcrest one with a trail which ends at £20) a friend and I nudged in three triple bars on reels 1, 3 and 4 and the machine held! Pressed Start and sure enough all four came in. A hold after nudge for a £100JP, first and only time I saw it. You can't even get a hold after nudge for £2.40 these days, bloody tight bastards!