You have mentioned that in your sales office, there are less than 10 employees
The act says that it applies to any establishment with more than 10 employees
Sec 2 (e) of the act says "establishment" means--
(i) a factory;
(ii) a mine;
(iii) a plantation;
(iv) an establishment wherein persons are employed for the exhibition of equestrian, acrobatic and other performances;
(iva) a shop or establishment; or
(v) an establishment to which the provisions of this Act have been declared under sub-section (1) of section 2 to be applicable;
Since the sales office probably have a shop and establishment license, it is covered in the definition above. If it has less than 1o employees, i suppose it is exempt.
However, you also need to check the shop & establishemnt act of your state because some of the states have put in additional clauses extending the applicability of the Maternity Benefit Act to offices with less than 10 employees.
In spite of the exemption, if your management is willing to follow the law, it is good. You can not make an assumption, so you should officially intimate them of the cases and ask whether they would like to cover the employees even if not strictly applicable