Librosa stft + istft - Understanding my output (which always seems too perfect) at varying window lengths
The information you think is missing, due to either poor visible frequency resolution or poor visible time resolution, is actually still contained in the sequence of FFTs, but not in a form that can be easily visualized, especially by just displaying FFT magnitudes or spectrograms.  That's because the information is "hidden" in the FFT phase results.  

In the sequence of short FFT windows case, some of the frequency resolution information is represented in the difference in phase between adjacent or overlapped windows.  In the long FFT window case, much of the time locality information is represented in both the absolute phases and in the difference in phases within groups of nearby FFT result bins.  None of that is visible in FFT magnitude plots or spectrograms; and FFT phase and phase delta plots are hard to read.

But complete complex IFFTs do use the phase information contained in the real and imaginary components of the complex FFT results, and thus can reproduce both the time and the frequency information accurately and completely.

This phase information can be used in certain forms of FFT analysis to gain back some of the "missing" resolution.  For instance, the phase vocoder algorithm deduces or uses greater frequency resolution by looking at the phase deltas between adjacent or overlapped FFT windows.  And the time shift property of the FT shows how the phases between DFT result bins rotate relative to each other as an event (an AM or "beat" modulation, etc.) is rotated to different positions within a DFT window.