The chronology of events in the sentence is guaranteed by the use of "but by". If you think of a simpler sentence with the same structure:
"In 1923, the tax rate was 15%, but by 1911 the tax rate was 11%"
that sentence makes no sense, because when we say "but by 1911..." in this way, what we mean is: "but by the time 1911 rolled around...". The time we're describing would need to come after 1923 if we say "but by...".
If you wanted to compare
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"In 1923, the tax rate was 15%, but by 1911 the tax rate was 11%"
that sentence makes no sense, because when we say "but by 1911..." in this way, what we mean is: "but by the time 1911 rolled around...". The time we're describing would need to come after 1923 if we say "but by...".
If you wanted to compare
...
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