If you go through the definitions about the applicability, in my opinion, gratuity is applicable in your case even if the number is less than 10 today, subject to the completion of 5 years of service by the individual. Look at the definitions:
An Act to Provide for a Scheme for the Payment of Gratuity
An Act to provide for a scheme for the payment of gratuity to employees engaged in factories, mines, oilfields, plantations, ports, railway companies, shops, or other establishments and for matters connected therewith or incidental thereto. BE it enacted by Parliament in the Twenty-third Year of the Republic of India as follows:
Section 1: Short Title, Extent, Application, and Commencement
(1) This Act may be called the Payment of Gratuity Act, 1972.
(2) It extends to the whole of India:
Provided that in so far as it relates to plantations or ports, it shall not extend to the State of Jammu and Kashmir.
(3) It shall apply to:
(a) every factory, mine, oilfield, plantation, port, and railway company;
(b) every shop or establishment within the meaning of any law for the time being in force in relation to shops and establishments in a State, in which ten or more persons are employed, or were employed, on any day of the preceding twelve months;
(c) such other establishments or class of establishments, in which ten or more employees are employed, or were employed, on any day of the preceding twelve months, as the Central Government may, by notification, specify in this behalf.
(3A) A shop or establishment to which this Act has become applicable shall continue to be governed by this Act notwithstanding that the number of persons employed therein at any time after it has become so applicable falls below ten.
(4) It shall come into force on such date as the Central Government may, by notification, appoint.
Section 3(b) clearly says "ten or more persons are employed or were employed." It is better to make the 5-year completed employees eligible to avoid further legal consequences.
Regards,
Ulhas Chandratre
Sr. HR Professional, Pune