It's not uncommon for established firms, especially those with a long history like chartered firms ( Association with Mastanaiah & Co / CH. Harikrishna / N. Sambasivarao & Co / Aaki & Co), to reach out to their alumni network for various purposes such as networking, keeping in touch, and potentially even for business opportunities

Networking: Alumni networks are valuable for networking purposes. They allow former employees to stay connected, share experiences, and potentially collaborate on projects or job opportunities in the future.
Maintaining Relationships: Keeping in touch with former employees helps the firm maintain positive relationships and goodwill. This can be beneficial for future recruitment efforts or even for obtaining references or recommendations.
Celebrating Milestones: Reaching a 50-year milestone is significant, and the firm may want to celebrate this achievement by reconnecting with past employees and acknowledging their contributions to the firm's success.
By requesting alumni to register, the firm can effectively manage and leverage its alumni network for various purposes, ultimately strengthening its connections and opportunities within the industry.