When providing more information about an event in the past, are we allowed to use present continuous?

While describing an event in the past, is it possible to use present continuous or present perfect continuous while still being grammatically correct? In order to explain my question a bit better, I have an example.

[On the topic of Britain’s Chain Home Radar Network before the start of World War 2] By the spring of 1939, there were 20 stations, providing a mostly unbroken electronic barrier from Ventnor near Portsmouth in the south, to Netherbutton in the Orkneys to the north.

For this example, is the bolded section grammatically correct, or would it be preferable to replace it with "were 20 stations that provided a mostly"?