This mythical 1000th F1 Grand Prix count gets no easier if you include the Non Championship F1 races, they were run to F1 rules - not Indy or F2 rules - so surely must count.
In the 1960's and into the 1970's Britain had quite a few NC F1 races each year. The International Tourist Trophy at Silverstone. Brands Hatch used to hold the International Race of Champions (usually in the "other" year when it wasn't hosting the GP). Oulton Park had the Gold Cup and Goodwood always had a Formula 1 race at its Easter Bank Holiday meeting. The last NC F1 race (for current GP cars) held in Britain was the 1983 Race of Champions - won by Keke Rosberg in the Williams. BBC TV showed it live.
In Sicily there were races at Enna, round Lake Pergusa. There was Syracuse - wherever that was, Pau and Albi in the early fifties, Solitude (Germany) of course, and Roskilde ring (Denmark). Some places had to hold a non-title F1 race before they could qualify for a title race (that was basically a rule. Warwick Farm's race was to be sanctioned in 1970 because of the successful running of Tasman events). There was also a NC race in Cuba in 1958. Before the race, Fangio was kidnapped by the Castro revolutionists, so he couldn't make the start.
If you take an overview of the varying estimates for NC F1GP numbers you get somewhere between 22 and 49+, so if you disqualify the non F1 rules races the 1000th race could still be China - or it may have been sometime last year - or it may fall in 2020 season.