Methods for data sample consistency

#1
Hello,

I would like to ask you for your opinion:

I have one data sample, let´s say with 600 units used for calculating some statistics (for example mean, std. deviation, q-o-q changes etc.) between the years 2006 and 2016. But from 2017 I would like to extend this data sample to let´s say 700 observations (with former units preserved).
Now I deal with a certain inconsistency because now I won´t be able to compare mean, std. deviation, q-o-q changes and so on. Those two time series 2006-2016 and 2017 onwards are now not comparable with data sample changed.
Are there any statistical methods or some transformation bridge of how to deal with this inconsistency to make possible to have one coherent time series?

Thank you very much for any comments.