How long do NFC tags work for ?
I'm using tags on a project that will need to work over a number of years. Will normal NFC tags still work or do I need active tags?
You need to consider two aspects to this. The first is the physical tag itself and the second is the NFC chip.
The physical aspect is, for example, the adhesive on the sticker or the plastic surface. If the tag is in exposed conditions where it might be subject to rain or freezing temperatures, then it can fail if it's not the right material. Using a simple paper face label for example in outdoor mountain wayposts is not likely to bring you much success. Therefore, consideration of the environment in relation to the choice of tag is important.
Having said that, a plastic face sticker attached to a clean, dry surface can last a very long time even if in a relatively exposed position. A plastic face label indoors can last for many, many years.
Secondly, the chip itself. Most NFC tags such as the NTAG series have a memory specification of 10 years. In reality, it's likely to be much more than that but that's the spec. If you need longer than 10 years, then you need to go for something like the ICODE SLIX which has a memory lifespan of 50 years.