I changed the coolant put in Nulon Red, read the fine print on the container, not suitable for brass/copper radiators, had to drain & flush and put in Nulon Green need to take care with reading the labels:D

I think the green coolant has 3 times more reserve alkalinity to stop the PH from dropping.
Low PH slowly dissolves brass.

Don't think fresh Nulon Red would pose any immediate risk to brass/copper radiators.

You are probably right, didn't want to risk it for a few dollars, good copper radiators could be hard to find