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is it possibile to have a system of WLCs controlling both 1242 and 1252 installed in different areas of a factory and (1250 at offices and 1240 at production site) managing the same WLANs?
This works with out a problem. so long as the code supports the AP, you can mix and match the AP' to your networks contect.
The latest 4.X and 6.X supports 1240 and 1250. You can mix both. You can verify by reading the Release Notes and it will tell you what AP's are supported by the firmware.