I bought a clone Yale item (Securit Standard Nightlatch - S1740.)
It came in the usual tight plastic wrapping on a card. There were no instructions. I did look at a video on You Tube that gave me some idea. I fitted the main body to the door, then the keeper on the other side, but then I realised that the bolt part is curved on one side and straight on the other - mine was the wrong way round. I then lost the plot and tried to modify and ended up with a dreadful mess of split wood and shavings from the door jamb and it was getting late and cold. I became totally frustrated and depressed and decided to leave it all for a clearer head next day.
I came in and ate my meal, but couldn't help puzzling about this problem and I knew I was overlooking something obvious. "Are these items left or right handed,." I was trying to imagine the lock fitting on a door that opened from the other side, but my brain is not very good at such spatial awareness imaginations, a sad failing for an aspirant DIYer. There was no indication on the packaging. At about 8:00 pm I suddenly thought "is that bolt reversible?"
Off I went to the shed in the dark armed with my torch. I unscrewed the main body of the lock from the door, turned it over and saw a tiny screw securing a backplate. I unscrewed and lifted the plate. A small spring jumped out like one of those miniature frogs I have seen so often on the Scottish hills. The spring landed on the decking and it took overt five minutes to find it in the dark. I brought everything back into the house, and after turning the bolt I tried to refit the spring but there was no way I could see how it went. I searched the manufacturer's website to no avail. They had no phone number, just the option to send an email. I typed my SOS to them and now await their reply.
Long live DIY.