None of this alters the fundamentals about the checkpoints to reality. Sure, they can drift from observed outcomes, but to the extent China (or any nation state) trades internationally, it's capacity to supply, and acquire goods and services and raw materials to meet external market demand present an objective reality.
Can you know if the published reserves are as large (or small) as suggested? No. But you can reflect on the terms of trade and decide if they are better or worse than you expected in the light of reality.
DPRK is supplying shells to russia for the war in Ukraine. This speaks both to the DPRK capacity to manufacture and supply shells, their quality (the rate of duds) and the industrial capacity inside the FSU such that it requires this to meet expected demand. These are the kind(s) of measures in reality which make it very unlikely sustaining "lies" about the economy can work long-term: Other people can draw their own inferences.
Planned economies set goals. China set specific economic goals. Failure to deliver has consequence. If they miss targets there is an internal conversation which in due course we hear about. If they exceed target there are consequences and a conversation in due course we hear about. If a goal is met but the next cycles goals are radically different that tells a story too: if your demand remains but they cannot supply, their prior ability to supply must have had consequences or some other aspect of the econnomy has changed.
In any event, planning an economy on false data is an exercise in peak frustration for the staff concerned. It's less likely anyone pushes paper for a fake outcome, the stakes are too high.
I view this as similar to differential analysis in cryptography. Heat of the chip die tells a story. Where the work is done tells a story. Remember, aircraft and satellites fly the world 24/7 so it's not like an open cut mine can be hidden, or the spoil heaps of a deep mine, and the extent they grow is governed by the laws of physics: you can only pile soil so high before you have to slope it. So even things as unlikely as overflight by remote sensing satellites can tell you about the fundamentals of mining, industrial activity.
"success" here has many measures. I'm focussed on the one which relates to the core topic, the economy. There are other measures, the demographics for instance which tell a tale of a cohort "missing" during the Mao famine years, and in due course will tell a tale of covid.