It's reprints. The Dennis and Gnasher annuals always used to be reprints from about 14-15 years earlier, although that changed with his 2009 reboot for a new CBBC TV series. (That unrecognisable version of the character didn't menace people intentionally and I don't want to read it.)
In other words, the strips in this book are 1980 vintage or so. They're also fairly good. It's a comfortable middle ground sort of Dennis. Slightly mediocre, but decent enough. This is long past the era of Davey Law and the slipper, sadly, but this Dennis is a terror without being as thuggish and bullying as he'd become for a while later. He perpetrates some amusing antics. ("We borrowed some manhole covers.") I enjoyed "Dennis's guide to etiquette".
1. I like Dennis's granny, who's a lot like him except that her spiky hair is grey.
2. Walter the Softy is quite a good character in his own right. His effeminate extremes of softiness add a surprising amount to this collection. (Compare with Dennis's horror at being forced to wear a dress in one of these stories.) I almost want to read a Walter book.
3. There are four stories in the first twenty pages where Gnasher gets ill and/or goes to the vet.
It's reasonably good. Being a reprint collection is a plus, because it makes the book denser. Annuals like this have a lot of pages to fill, so one often sees stories with only a few panels per page. This, on the other hand, is full of two-pagers from the magazine. Result: more jokes and ideas. I quite liked it.