Okay, it seems unclear whether the TowerX value is also present on the mast or just an internal numbering in the data set. Personally, I would mark values from the mast as ref:US:eff and use the unsigned_ref:US:eff key in the second case. I personally see the source:ref key as problematic because the attribution key was used instead of source. But you are welcome to discuss this on your standard channels, but please don't invent any new formation logics (such as source:eff_ref). 

The additional note for the values of the ‘surveillance:type’ key is also appropriate. The standard values are written in lower case. And AI is not a visible sensor but describes the data processing of the recorded data. I would generally delete this value, as it cannot be validated.