If you have that kind of logic then, it will be better to say : no one is ever entirely 100% "sure" about anything related to military developments.
I mean your logic can be applied to every country in this world.
If you need a solid proof, it would be a war, where all military development can't lie.
Spy can only provide a little information if you compare that to all military development.
I think military development is top secret for all country, whether it is a " weak " or " strong " country.
Technically speaking, that is true, however the difference in the degree of up to date and reliable information we have about Chinese military developments is significantly lower than that of other countries, which we typically have far more up to date and open knowledge about.
Obviously I'm not arrogant enough to suggest that being "100% sure" about a new military development means knowing all of a weapons systems specifications, reliability and performance, and weaknesses and strengths... I was talking about much more general things, such as whether a new weapons system is being developed at all, a weapons name, its intended use, its manufacturer, general performance parameters.... things which are generally given to us by very official and reliable sources for military developments in western countries and others. I'm not sure if you're taking my statement in its very literal meaning accidentally or if you're being deliberately pedantic.
Realistically I can't imagine that you thought I was suggesting we should all have 100% full knowledge of every military development for every nation from how the lowest grunt is kitted out to the most secretive nuclear dispersion and doctrine of a nations' nuclear arsenal and everything in between.
That is why I used the phrase "military development" -- referring to some general information about the newest occurrences which will typically be described by official sources for general public consumption. I should be more accurate to say "military information," as it the information obviously does not have to relate to new occurrences or weapons but also events in the past or existing weapons systems.
In other words, I was using that phrase "100% sure" to illustrate the reliability (or rather lack of reliability) of information from official sources about the Chinese military, compared to information of a similar nature from other nations. That is to say, sources from other nations may be able to make statements about their own new military developments, and the reliability of the source may be considered very accurate and reliable, while for Chinese military watchers, there is not only a very small number of reliable sources, but there are also a significant number of unreliable sources that mingle with the few reliable sources we have. That means we have to be constantly vigilant about the validity of new statements and claims about the Chinese military (more so compared to other nations), and appreciate that very often, accepted information may change if a new rumour from a big shrimp appears or if some new off hand statement by a PLA officer occurs.
This isn't to say there are no unreliable sources for the military forces of other nations either, but they tend to have far less uncertainty surrounding many military developments compared to China, and there also tend to be a larger number of sources whose reliability will not be challenged.
The fog of war is there for everyone, but some nations further add to the uncertainty, by being far less open about their military developments than others. If you're denying that there is a vast difference in certainty about the newest military developments in China compared to their counterparts in western countries, then I'm not sure what to say. Maybe you haven't read this forum for long enough.