Historically, countries almost never understate the strength of their armed forces because that would invite pointless conflicts with weaker adversaries. Unless the former is looking for some casus belli to invade the latter, it leads to the most pointless loss of life where the latter never stood a chance anyway but the former has to waste resources on the defense.
I don't know how that calculus changes in the context of modern superpowers or China's ambitions for Taiwan but that's the reasoning historically.
How can you possibly know how much a country spent on military to conclude they almost never understate their funding?
A perfect reason a country may understate their military spending is to hide their capabilities. For that matter, they may overstate their spending as well.
I don't know how that calculus changes in the context of modern superpowers or China's ambitions for Taiwan but that's the reasoning historically.