As stated above, neither Cuttlebones or Mineral Blocks have an expiration date, assuming that you are using natural, plain versions of both and not flavored ones that have artificial flavors, colors, etc. in them (such as the fruit-flavored Cuttlebones and/or Mineral Block, which may actually have an expiration date that should be listed on the packaging). Natural, plain Cuttlebones and Mineral Blocks are good as long as they last, and only need replaced when your birds finish them off...
One thing to keep in-mind about both Cuttlebones and Mineral Blocks is that each are extremely porous, and as such, if they happen to get bird poop or anything else on them (as they often do), it's going to soak into the Cuttlebone and/or the Mineral Block, so if this happens then they should be removed immediately and replaced, as bacteria is going to immediately start growing in and on them, and this can easily make your birds sick if they eat it...