Not quite true, there were limits particularly since Ibrox, but the science and understanding of crowd behaviour was in its infancy so most stadia capacities were based upon square meterage of terrace and number of seats rather than evacuation times, human behaviour etc. The green guide changed a lot of this when published after a series of major incidents in the 70's and 80's and then stadia became designated and under the control of the Local Authority who have to issue a Safety Certificate. The assessments these days take many factors into account and result generally in much lower capacities than were allowed some years ago. In a ground like ours it is highly likely that the overall stadium as measured could hold more than its actual limit but exit routes, widths, segregation measures, areas of roofing even dictate matters.
Back in the 70's I recall Moss Lane as having an arbitary figure of 10,000, that was with the away end being a grassed bank as was the mausoleum, and no barriers anywhere. Doesn't bear thinking about but it would then, if it came to it, have been up to the local plod, who have/had no experience or proper training in such issues.