I'd advise raise a CSE with NDVO first abt updating change of employment...then depending on their reply (if they ask you to contact Poland VO instead)-
Send the Form with Updated Employment History, Relieving Letter of old company, and Joining Letter of ur new company...
Explain in a cover letter (draft this carefully) that there was a delay/confusion in processing ur Final working date on your Relieving Letter....and you were still working on transition for the next 7 days hence you didn't update the Employment Change Details at the time of sending application but later the company processed your Relieving Letter with final working date as 31st only.....Be extremely polite and add a line abt sincere apology- not meant to misrepresent in any way....As long as u act fast and inform the VO quickly on your own, I feel it'd be fine...they r experienced ppl, they'd have seen the multiple issues ppl face at their workplaces over the years...
Experienced Seniors please comment further if your opinion is different...