Stata -- extract regression output for 3500 regressions run in a loop

I am using a forval loop to run 3,500 regressions, one for each group. I then need to summarize the results. Typically, when I use loops to run regressions I use the estimates store function followed by estout. Below is a sample code. But I believe there is a limit of 300 that this code can handle. I would very much appreciate if someone could let me know how to automate the process for 3,500 regressions.

Sample code:

forval j = 1/3500 {

    regress y x if group == `j'
    estimates store m`j', title(Model `j')
}

estout m* using "Results.csv", cells(b t)   ///
   legend label varlabels(_cons constant)   ///
       stats(r2 df_r N, fmt(3 0 1) label(R-sqr dfres N)) replace