The Slammiversary number is just about identical to the 1,400 estimated buys that ROH's Best In the World pay-per-view drew on June 28. It was noted that the numbers between the two events are so close that there were just six buys separating the shows in one major cable conglomerate. It should be noted that most of the ROH viewership comes from the subscription streaming service, which provides a better price point. Impact viewership comes from either TV pay-per-view or FITE TV, both at the same price point, which means most of their viewership would be TV pay-per-view.
To compare the Impact numbers, the 2018 Slammiversary 16 pay-per-view drew an estimated 1,500 buys while Rebellion drew an estimated 2,000 buys and Homecoming drew an estimated 3,100 buys.
The Observer also reported that of the 1,500 Slammiversary buys, an estimated 8.75% purchased WWE Stomping Grounds while an estimated 30.00% purchased AEW Double Or Nothing, an estimated 7.5% purchased ROH Best In the World, and 6.3% purchased UFC 235.
On a related note, The Observer reports that last Sunday's Slammiversary pay-per-view drew around 850 fans to Gilley's in Dallas, Texas, which was a full house the way the arena was set up. PWInsider reported "roughly 1,000 fans" in attendance with 700 tickets sold in advance.