Use unsigned version format. This way can use one additional bit, and when encountering invalid revlogs with the first bit set don't produce python warnings or strange error messages.

#!/bin/sh

hg init
touch a
hg add a
hg ci -m "a" -d "1000000 0"

echo 123 > b
hg add b
hg diff --nodates

hg diff --nodates -r tip

echo foo > a
hg diff --nodates