What's the true value of a stock?

High valuations of unlisted companies make it hard to value listed companies

What's common to Hyundai, Johnson & Johnson, Samsung and Patanjali?  All of them are big players in their respective sectors.  All are unlisted in India. The lack of listing is frustrating.  It eliminates the Peter Lynch type of investment where a consumer buys both the brand and the company. 

For example, a consumer may compare equivalent Hyundai and Maruti models before buying a car. A Lynch follower would like to buy shares in the company from which she bought the car. But you can't buy an unlisted company or even compare financials with peers, given the lack of information. That also