The open jar icon is usually seen on a lot of products. The icon is usually accompanied by M (months), W (weeks) and 12M (12 months). The icon represents that after this time period, the product will no longer give the same effects after opening the seal of the product.
We all have seen lots of blank pages at the start or end of a book. The reason of it is that books aren’t printed on separate pages. Instead they are printed on a large sheet. The large sheet contains pages of a book which is then divided into smaller pages. The space which is left due to lack of content become blank pages in a book.