Looking at the races where I remember being near Warwick at the finish, we have about the same elapsed time, so I would say you are dead right. Either the sloops should have an extra 5 minutes or the cats should have 5 minutes less. It's probably the later, since the sloops started first and that's when they probably started the timer on the committee boat.

This is why it's always bad practise to use elapsed times when recording finishers. If actual start and finish times are recorded and software used to calculate the elapsed times this kind of mistake doesn't happen (and it's so easy to record real times - you only need a wristwatch).

When elapsed times are recorded stuff-ups often happen (like this, or the timer accidentally gets reset during the race, or it falls overboard or someone spills their beer into it or the battery goes flat or .....).

Fortunately it doesn't actually affect the results.

Not sure I feel like going right through that page of results adjusting all the times though - took long enough to build it in the first place