Data on Nest Plus for futures and options is stored on the server in sequence of near-month, next-month, and far month. Let us consider the months September/October as examples. Until expiry date, September was the near-month contract. All September derivative contracts expired on the date of expiry, and October became the new default near-month contract.
Remember, to get a continuous stretch of data, we map the data by near-next-far month... This is just the way it is. It's standardized.
Until the date of expiry, September was the near-month contract, but after it got expired, October is the near-month contract. So in October's chart, till the day of expiry it will show September's data and from the start of the new contract month, it'll show October's data.
About the mismatch of data other than expiry, if you could give us examples, we'll surely look into it.
If that is the way you treat the data, I have no issues. If for NIFTY13OCTFUT, we see NIFTY13SEPFUT till the 26th of Sep, and NIFTY13OCTFUT from 27th onward (i.e. as a continuous contract), that is fine.
If you will assume that I understand near/mid/far month, maybe closure may be quicker. Perhaps I did not explain clearly.
In the image, the left table is from Vwap Statistics window of ZT for Crude. The data was taken to Excel so that it could be presented more clearly. On the right, is the data table for Crude from Nest Plus.
It is expected that the data matches. If you adopt continuous contracts as "standardized", then both the sources of data should be the same. However, they match after the 20th. The data prior to the 20th does not match. This is where the request to be consistent arose.
Also, if I am not mistaken, this did not happen during the previous expiry. When Nifty Aug rolled over to Sep as the near month contract, the Plus data continued to show the same contract data, i.e. NIFTY13SEPFUT when it was mid month and when it was near month (that is as a discrete contract). This seems to have changed only from the NIFTY13OCTFUT contract. If this observation is correct, that's just the way it is has changed recently. Maybe you could use your good office to verify this with Omnesys, and if they will continue to apply this principle.
Also, I imagine this applies to futures only, and not to options.