Worried About TCS Background Check? Will My Unregistered Ex-Employer Cause Issues?

I got a job in TCS-BPO, Kolkata. However, my previous company was unregistered. I worked there for 4 months as a Senior Executive-Marketing and received a good hike in my salary at TCS. I just want to know if this will create any kind of problem in the TCS Background Check (BGC) or if it is possible that I will lose my job at TCS after the BGC and they will blacklist me?

If your company remains unregistered, that's not your fault. What is the proof of your employment that you received from them? What are the points of reference that you have offered to TCS? Looking forward to hearing from you.