Company Search really max results 1000?

I am implementing PHP script for private use to monitor similar names being registered
It works fine on text searched where Total_results is < 1000
But if total_results is larger, then the response is a valid PHP array up to 1000 and nothing afterwards
This simple debug check shows what happens :-
Where first digit is pass number (for pages of 100 items) and 2nd digit is the start_index
0-0
response is array
6379
1-100
response is array
2-200
response is array
3-300
response is array
4-400
response is array
5-500
response is array
6-600
response is array
7-700
response is array
8-800
response is array
9-900
response is array
10-1000
response is NOT array
string(0) “”

Given there is no code change and just an incremented query, is this an API limitation ?

If it is the case that the API limits number of results, that can be understandable.
But I have seen no documentation of it.
Documentation would be helpful, or even just a meaningful response to the query rather than an empty string.
Would be helpful to declare the limitation, so that we don’t waste hours examining code for problems which don’t exist.

@MArkWilliams or @amaddaford : would you be able to confirm that there is a 1000 limit on results so we can close this off ?

Many thanks