Nobody replaces a garment on the day it stops looking right. They replace it when somebody finally says something, which means the standard you actually run is set by whoever is least willing to raise it.
The fix is not a rule about how long a garment lasts — that depends on the garment, the role and how it is laundered, and any number attached to it would be wrong for most people. The fix is deciding who is allowed to say a garment is worn out, and making it a normal thing to say rather than a complaint. In practice that is usually the wearer, with a manager confirming rather than assessing.
The second half is making sure the replacement matches. A garment ordered two years after the original, from a general description rather than the record, is where a range quietly becomes two ranges.
A replacement that does not match is a new uniform, not a replacement.