Such a wonderful question you have asked. I was looking for a way to up-vote your question but there seems to be none.
Golden knowledge like what Benjamin Graham propounded will defy compartmentalisation to a particular situation and will certainly attain a global hue. Yes it indeed applies for purchasing businesses also and indeed I apply the rules in evaluating acquisition deals I craft.
Conversely, Warren Buffett compares purchasing even a single share in a company to that of purchasing the whole business - applying the same caution, prudence and analysis - reinforcing your concern and my answer.
Buying a share and buying an entire business are one and the same and the same knowledge, care and patience shall exercised in both the situations - there is no room for even a shred of doubt or confusion about this.
You have asked me a question that has not occurred to me, nor has anyone asked me so far, but it is indeed a great question and I highly appreciate that you have raised it.