Checking a Representative Sample of Mezuzot

Question:

We bought all our mezuzot at the same time, and we were told that they were written by the same very well-known expert sofer scribe. Surely, it should be enough to check a representative sample in order not to have to check each one?

Answer:

One must check every mezuzah. Each one of them is placed in its own distinct environment and conditions. Moreover, the ink and parchment of each are organic materials that might react differently to humidity and heat fluctuations.[1]

[1] Birkei Yosef 291:1, cited in Agur B’Ohalecha 32:9; Kevias Mezuzah K’Hilchasah 14:3:7.