Is there a plate on an octavia to signify what week and year it came of the production line? If not any way of finding out?

Skoda should be able to tell you if you call them. But most cars the majority of important information like this is on a sticker in the drivers/passenger door sill or on the door itself. I'm sure I've seen someone say the build week info for the O3 is on a sticker on the passenger door but don't quote me on that. It's also possible to do it from the VIN too but I've no idea how.

If you google 'VIN decoder' there are a few basic decoders that will tell you the build week etc. A dealer can do the same through skoda's systems.