Gurumurthy Sir, his question is slightly twisted.
He says the contract workers worked for more than 20 years at the same location, but under different contractor. Each contractor was for less than 5 years and therefore individually not liable for gratuity. But is the principal employer liable because they worked at his factory for 20 years.
Incidentally the act does not say principal employer is liable for gratuity, only pf, ESIC, wages, bonus, minimum wages. But spurts have granted it as liability if principal employer.
So, your opinion will be appreciated in light of the above.