This doesn’t explain why the argument is vulnerable to criticism. Even if there are years when there’s no change in the CPI, the author still jumps to the conclusion that government benefits are sometimes too high because they don’t account for production costs.

The author doesn’t list every single good and service that’s included in the CPI, but this isn’t a flaw in his argument. We know that the CPI detects monthly changes in the retail prices of goods and services overall.

This doesn’t explain why the argument is vulnerable to criticism. Even if some people use retirement benefits to purchase unusual goods and other people don’t, the CPI is still used to account for overall changes in the average cost of living.

The author doesn't draw an inference from what has been true in the past, nor does he make a conclusion about what will be true in the future. He concludes that government benefits are sometimes too high based on a claim about technology lowering production costs.

The author talks about the CPI, which measures changes in retail prices. He then draws a conclusion based on technology that may lower production costs. But we have no idea whether it would impact retail prices, and the CPI accounts for changes in retail prices anyway.