How can you accurately estimate the number of tickets SOLD since that is not published on my lottery’s site?

This answer depends on the data published on your lottery’s website.  Most lottery websites do not publish the amount of tickets sold.
We’ll use the Arizona Lottery as an example of how we can work calculate the number of tickets sold.
We are able to track how many tickets have sold based on three key data points that the AZ lottery DOES publish:
1) The AZ Lottery provides the total number of prizes remaining at all prize points (from the top prize down to the lowest prize). For example for $1 Decade of Dollars, there are currently 668,067 $1 prizes left on 5/3/18.
2) The AZ lottery publishes the DETAILED odds for every Price Point. For the same game, the odds of winning $1 is 1:8.   This is a fixed value at the time they create the game and doesn’t change over time.  But the prizes remaining does change from day to day.
3) The third data point is WHEN they publish this data.  This is the data point I can’t show you – it is our CODE that scrapes the data from the lottery EVERY SINGLE DAY.  On the first day that a game is published, the first day we scrape it, the PRIZES REMAINING for each prize point would be the MAXIMUM number of prizes.
On the first day, (for example only), the prizes remaining for winning $1 may have been 800,000 tickets.   We multiply the detailed odds times the PRIZES remaining – that gives us the total number of tickets printed. For just the $1 prize, it would have been 8*800,000 =6,400,000 tickets because the odds are 1:8 and the total prizes remaining on day 1 = 800,000.
We store that number in our database.
Then, each and every day, we re-scrape the PRIZES REMAINING posted on the AZ website, do the calculations and compare that to the original total number of tickets printed.  This gives us the Estimated % sold on any given day, directly from data on the AZ Lottery website.
NOTE – We have to do this differently for each state lottery based on the data they do provide.  For your state, we may have to provide a different method to get to the estimate % sold, but the facts are the same – a combination of data provided by the lottery website, combined with daily data mining and data analysis helps our customers get deeper analysis on picking the very best game!